How to possibly prevent cylinder scoring
Discussion
hartech said:
For the cylinder wall to get so hot on one side that the engine piston scores must require (IMHO) some bubbling of the coolant on the surface of the outer cylinder wall and this usually only occurs when coolant speeds would be very slow indeed and bubbles would naturally rise to the top (the thrust side on bank 2 – not on bank 1). But it would also need high piston to cylinder wall forces as well to squeeze out the oil film and make hard contact between the piston and Lokasil bore.
How about fitting steam vents on the upper side of the block?As you may know it's a common mod on 944T that are prone to blow the headgasket on the 4th cylinder as the head has a cavity in which steam can be trapped if the system hasn't been bled correctly. On high end builds the 2V head still sees coolant turn into steam and several vents are added.
Hi Baz
I am reading with interest re the engine problems that these cars suffer. I am looking at may be getting a Cayman S some time in the next 12 months and this does concern me a little. Out of interest do products like water wetter help with this kind of problem? I have raced a Westfield for the last five years with a highly modified 2000cc Vauxhall engine fitted and a small radiator to save weight. I have used water wetter to good effect keeping the engine temps under control even though the engine was making over 280bhp and a radiator designed for a 1000cc VW Polo. It's just a thought and I am sure it's already been tried.
Cheers Matt
I am reading with interest re the engine problems that these cars suffer. I am looking at may be getting a Cayman S some time in the next 12 months and this does concern me a little. Out of interest do products like water wetter help with this kind of problem? I have raced a Westfield for the last five years with a highly modified 2000cc Vauxhall engine fitted and a small radiator to save weight. I have used water wetter to good effect keeping the engine temps under control even though the engine was making over 280bhp and a radiator designed for a 1000cc VW Polo. It's just a thought and I am sure it's already been tried.
Cheers Matt
Great stuff. My own, updated 'shopping list' of ideas for simpler fixes to the issue, mostly intuitive...
1 The lower temp engine thermostat. (got this now, phew, thanks Baz)
2 An electric in line water pump to increase the coolant flow to the front radiators once the temp reaches a certain level in the front pipework. Obviously as a failsafe the pump should not restrict flow when off. No idea how to achieve all this -at the moment but the pumps exist on ebay -drag racer kit I think, for whom heat build up is a tad quick...!
3 Centre radiator for extra cooling.
4 A reduction in the temperature at which the stage 1 radiator fans cut in. No idea how to achieve it without by passing the existing circuits, which of course is an easy fix, but it would be neatest to have the cars ECU set to a lower temp, eg 95c for cooling fan start up.
5 Modified front wheel arch liners (to latest 997 GT3 design) to induce higher air flow through the front radiators at low driving speeds. Will do this soon and will probably copy the GT3 cut-out design. Also thinking about trying some guide vanes in the front face of the rad.
6 A reduction in the temperature at which the engine bay fans start up, ECU fix?
7 Faster water pump pulley -any further on investigating this Baz?
8 Increase the % water content in the coolant (water has twice the thermal capacity I hear!)
Anyone got any more ideas
1 The lower temp engine thermostat. (got this now, phew, thanks Baz)
2 An electric in line water pump to increase the coolant flow to the front radiators once the temp reaches a certain level in the front pipework. Obviously as a failsafe the pump should not restrict flow when off. No idea how to achieve all this -at the moment but the pumps exist on ebay -drag racer kit I think, for whom heat build up is a tad quick...!
3 Centre radiator for extra cooling.
4 A reduction in the temperature at which the stage 1 radiator fans cut in. No idea how to achieve it without by passing the existing circuits, which of course is an easy fix, but it would be neatest to have the cars ECU set to a lower temp, eg 95c for cooling fan start up.
5 Modified front wheel arch liners (to latest 997 GT3 design) to induce higher air flow through the front radiators at low driving speeds. Will do this soon and will probably copy the GT3 cut-out design. Also thinking about trying some guide vanes in the front face of the rad.
6 A reduction in the temperature at which the engine bay fans start up, ECU fix?
7 Faster water pump pulley -any further on investigating this Baz?
8 Increase the % water content in the coolant (water has twice the thermal capacity I hear!)
Anyone got any more ideas
Some great positive and intelligent suggestions recently - most of which would/could make a difference and many would probably solve the problem - however all involve major changes to cars that do not yet have the scoring problem and the trouble is that most owners I would not expect to incurr the expense and inconvenience until it is too late when they realise perhaps they should have done. Many are blinded by the product's reputation and cannot believe the reported danger until it hits them.
Indeed most don't seem to find out about all this until it is too late and research who can fix it.
The take up of the low temperature thermostat has been extremely small (despite the obvious advantages, low cost and reported benefits) - so on that basis I was trying to think of something simple - that costs nothing - that owners might just hear about and manage to follow to help avoid damage - just simply to restrain themselves from too much enthusiasm on opening imediately up after a spell at rest when the engine had been used hard before the stop.
Baz
Indeed most don't seem to find out about all this until it is too late and research who can fix it.
The take up of the low temperature thermostat has been extremely small (despite the obvious advantages, low cost and reported benefits) - so on that basis I was trying to think of something simple - that costs nothing - that owners might just hear about and manage to follow to help avoid damage - just simply to restrain themselves from too much enthusiasm on opening imediately up after a spell at rest when the engine had been used hard before the stop.
Baz
911Fiddler said:
Here is the BMW electronic thermostat. No idea how it works, had thought it was a servo....
Electric stats are a good idea but need a bit of controlling from an ecu. I know the VW electronic stat has sensors both side of the stat to check its operating correctly. The stat opens early when full throttle is applied to produce maximum power and when on light throttle cruising it slows its opening to run the engine hotter for better emissions. I would think a retro fit to a car could be expensive and and possibly not that easy. Still the idea is sound if it could be integrated with the can bus system so the stat knew when the car was slowing down on light throttle and could open early to allow for a cooler running temp when idling.
hartech said:
...suggestions recently - most of which would/could make a difference and many would probably solve the problem - however all involve major changes to cars...
...I was trying to think of something simple - that costs nothing - that owners might just hear about and manage to follow to help avoid damage - just simply to restrain themselves from too much enthusiasm on opening imediately up after a spell at rest...
Baz
I for one wouldn't consider, say, a lower-temp thermostat, third radiator, and some water-additive as major changes and would readily have these items fitted if they reduced, or better still eliminated, the likelihood of scored bores....I was trying to think of something simple - that costs nothing - that owners might just hear about and manage to follow to help avoid damage - just simply to restrain themselves from too much enthusiasm on opening imediately up after a spell at rest...
Baz
If the 'Wetter' product really can 'reduce temps by 20degs', and reduce cavitation and bubbling, would this be enough of a temp drop (perhaps in combination with your thermostat) to cool the cylinders sufficiently?
Baz, are these types of changes sufficient, do you think, to eliminate the need to avoid WOT from a standstill without the risk of cylinder/piston damage?
Baz
Could you expand on the benefits of a low temp thermostat as I thought that once the car was up to temperature and the thermostat was open that it stayed open and that the only effect the low temp thermostat would have would be to slow down the time it took for the engine to get up to operating temp? Would be interested to know more about this?
Could you expand on the benefits of a low temp thermostat as I thought that once the car was up to temperature and the thermostat was open that it stayed open and that the only effect the low temp thermostat would have would be to slow down the time it took for the engine to get up to operating temp? Would be interested to know more about this?
Can't agree with everything you say.
That low temp t-stat may not be the cure all you think it is.
Tests have shown that as the engine temp goes down wear increases and fuel consumption increases.
Here are some numbers:
Temp Wear (cylinder) Fuel Consumption (GPH)
70F 0.008" 3.8
120F 0.002" 3.5
155F 0.001" 3.2
180F 0.0005" 2.9
210F 0.0003" 2.8
Next even though the coolant stream is split into multiple (12) streams and the coolant flows slower each stream is responsible for cooling a smaller region of the engine.
Furthermore, slower coolant speeds in the engine can actually improve cooling as the coolant spends more time flowing past the hotter regions of the engine. These hotter regions are quite small. If the coolant speed is too high the coolant can pass by/over the hotter areas without picking a good load of heat.
Plus it is a common feature in some areas of the coolant passages that coolant nozzles (which are
precision cast into the head) are used which carry coolant from a larger passage to an adjacent but
smaller passage. One end of the nozzle has holes that direct the coolant right at the hottest area
(generally at the exhaust valve seat area). This results in a localized increase in coolant flow speed and circulation which maximizes cooling.
Low coolant speed alone does not result in coolant bubbling (flashing to steam). There has to be
sufficient heat and insufficient pressure for this to happen. My info is that for every one psi increase in cooling system pressure the boiling point of the coolant is raised by 3F. If the system were pressurized to say 15psi the boiling point of the coolant would be raised 45F. The coolant temp could approach 250F and still not boil. At this temp though both radiator fans would be on high speed and would have been at this speed since the coolant temp climbed above 216F or thereabouts.
Next throttle bufferfly valves do not shut immediately. The E-gas controller slows the speed of the
butterfly closure for various reasons: to reduce wear/tear on the butterfly valve shaft/bearings and lower emissions. But this delay in closure means some air flows through the intake and chambers and help remove heat from the combustion chamber and exhaust valves and piston crown.
The engine is spinning at a good clip so coolant flow and oil flow (and oil in most cases is in closer contact with the hotter portions of the engine than coolant) are high so there is considerable cooling taking place.
The oil jets are aimed to spray oil at the underside of the piston. IIRC Porsche has claimed these oil jets reduce piston temps by 50C. This oil can't but help supply extra lubrication -- over and above what the crankshaft/rods sling about -- to the piston/cylinder wall interface.
The oil supply to these jets is controlled by a pressure valve. If the oil pressure drops too low the valve closes to reserve oil pressure and flow for the main bearings. I have to assume the oil pressure though in an otherwise healthy engine and with reasonably fresh oil and of the proper type and SAE viscosity would not have oil pressure dropping so low as to cause this valve to close and cut off oil flow to the piston jets.
Not sure where this belongs but under hard load not only is the piston temp elevated but so is the cylinder's temperature. Sure the cylinder is surrounded by coolant but the cylinder wall's diameter does increase some which helps maintain a suitable clearance between a hot (and larger) piston and the cylinder and its wall in which it resides.
Your scenario of an engine being under high load then going to tickover is a very contrived one. I can't see this happening except in two possible cases: On the track if the driver loses control of the car and ends up in the gravel and avoids engine stall. In this case he is unlikely to move the car off subjecting the engine high loads. The other case could be a driver could make a hard acceleration run then make a sudden stop, perhaps doing a 0mph to 100mph to 0mph test, repeatedly. But car mags which do these tests have not reported any problems with any cars, let alone Porsches.
The T-stat would be quite fully open due to the hotter coolant temp that results from the engine being under high load. These cars are pretty good at keeping themselves cool at road speeds and there are radiator fans which come on if road speed and air flow through the radiators allows the coolant temp to creep up.
My info is the T-stat is located at the output side of the water pump. Cooled coolant flow from the
radiators to the engine is not restricted by the T-stat (at least not directly). The cooling system is filled with fluid so any increase in flow/pressure at the water pump from it spinning up or from the t-stat opening up would result an immediate increase in flow of cooler coolant, coolant that had made its way through a radiator and shed its heat load. Fluid does not compress so a change in pressure at the output side of the water pump/t-stat would be instantly reflected at the coolant inlet of the engine and through the cooling system.
Porsche owners in the UK have it easy with that area's generally mild temps. Here in the USA with generally considerably hotter ambient temps -- how many days have temps been over 100F in some regions of the USA's mid-west region? -- there does not seem to be any significant number of cars (Porsches or any other brands of cars) suffering from the effects of being driven in high temps and I'm sure being subjected to the type of usage you believe can lead to scoring.
If the engine was as weak as you state cylinder wall/piston scoring would be only one result and probably the least severe. Total engine failure would be more likely as the metal to metal contact you suspect is taking place would result not only in scoring (at least at first) but ring and piston failure as the scoring allowed combustion chamber gases (and heat) down along side the piston/cylinder wall which would only exacrebate the problem as this destroyed the oil film at this interface and heated the piston up even further.
I do not doubt that in some few cars some cylinder wall scoring has taken place. I suspect it is from a manufacturing defect coupled with a reduction in the amount of time these engines are run at the factory.
In the past this wall scoring would probably have been identified and dealt with at the factory. But now, unfortunately for a few owners, it is they that sometimes find out this has happened.
There can be reasons to limit hard launches with any car including Porches, but piston/cylinder wall scoring is not one of them.
Sincerely,
Rockster.
That low temp t-stat may not be the cure all you think it is.
Tests have shown that as the engine temp goes down wear increases and fuel consumption increases.
Here are some numbers:
Temp Wear (cylinder) Fuel Consumption (GPH)
70F 0.008" 3.8
120F 0.002" 3.5
155F 0.001" 3.2
180F 0.0005" 2.9
210F 0.0003" 2.8
Next even though the coolant stream is split into multiple (12) streams and the coolant flows slower each stream is responsible for cooling a smaller region of the engine.
Furthermore, slower coolant speeds in the engine can actually improve cooling as the coolant spends more time flowing past the hotter regions of the engine. These hotter regions are quite small. If the coolant speed is too high the coolant can pass by/over the hotter areas without picking a good load of heat.
Plus it is a common feature in some areas of the coolant passages that coolant nozzles (which are
precision cast into the head) are used which carry coolant from a larger passage to an adjacent but
smaller passage. One end of the nozzle has holes that direct the coolant right at the hottest area
(generally at the exhaust valve seat area). This results in a localized increase in coolant flow speed and circulation which maximizes cooling.
Low coolant speed alone does not result in coolant bubbling (flashing to steam). There has to be
sufficient heat and insufficient pressure for this to happen. My info is that for every one psi increase in cooling system pressure the boiling point of the coolant is raised by 3F. If the system were pressurized to say 15psi the boiling point of the coolant would be raised 45F. The coolant temp could approach 250F and still not boil. At this temp though both radiator fans would be on high speed and would have been at this speed since the coolant temp climbed above 216F or thereabouts.
Next throttle bufferfly valves do not shut immediately. The E-gas controller slows the speed of the
butterfly closure for various reasons: to reduce wear/tear on the butterfly valve shaft/bearings and lower emissions. But this delay in closure means some air flows through the intake and chambers and help remove heat from the combustion chamber and exhaust valves and piston crown.
The engine is spinning at a good clip so coolant flow and oil flow (and oil in most cases is in closer contact with the hotter portions of the engine than coolant) are high so there is considerable cooling taking place.
The oil jets are aimed to spray oil at the underside of the piston. IIRC Porsche has claimed these oil jets reduce piston temps by 50C. This oil can't but help supply extra lubrication -- over and above what the crankshaft/rods sling about -- to the piston/cylinder wall interface.
The oil supply to these jets is controlled by a pressure valve. If the oil pressure drops too low the valve closes to reserve oil pressure and flow for the main bearings. I have to assume the oil pressure though in an otherwise healthy engine and with reasonably fresh oil and of the proper type and SAE viscosity would not have oil pressure dropping so low as to cause this valve to close and cut off oil flow to the piston jets.
Not sure where this belongs but under hard load not only is the piston temp elevated but so is the cylinder's temperature. Sure the cylinder is surrounded by coolant but the cylinder wall's diameter does increase some which helps maintain a suitable clearance between a hot (and larger) piston and the cylinder and its wall in which it resides.
Your scenario of an engine being under high load then going to tickover is a very contrived one. I can't see this happening except in two possible cases: On the track if the driver loses control of the car and ends up in the gravel and avoids engine stall. In this case he is unlikely to move the car off subjecting the engine high loads. The other case could be a driver could make a hard acceleration run then make a sudden stop, perhaps doing a 0mph to 100mph to 0mph test, repeatedly. But car mags which do these tests have not reported any problems with any cars, let alone Porsches.
The T-stat would be quite fully open due to the hotter coolant temp that results from the engine being under high load. These cars are pretty good at keeping themselves cool at road speeds and there are radiator fans which come on if road speed and air flow through the radiators allows the coolant temp to creep up.
My info is the T-stat is located at the output side of the water pump. Cooled coolant flow from the
radiators to the engine is not restricted by the T-stat (at least not directly). The cooling system is filled with fluid so any increase in flow/pressure at the water pump from it spinning up or from the t-stat opening up would result an immediate increase in flow of cooler coolant, coolant that had made its way through a radiator and shed its heat load. Fluid does not compress so a change in pressure at the output side of the water pump/t-stat would be instantly reflected at the coolant inlet of the engine and through the cooling system.
Porsche owners in the UK have it easy with that area's generally mild temps. Here in the USA with generally considerably hotter ambient temps -- how many days have temps been over 100F in some regions of the USA's mid-west region? -- there does not seem to be any significant number of cars (Porsches or any other brands of cars) suffering from the effects of being driven in high temps and I'm sure being subjected to the type of usage you believe can lead to scoring.
If the engine was as weak as you state cylinder wall/piston scoring would be only one result and probably the least severe. Total engine failure would be more likely as the metal to metal contact you suspect is taking place would result not only in scoring (at least at first) but ring and piston failure as the scoring allowed combustion chamber gases (and heat) down along side the piston/cylinder wall which would only exacrebate the problem as this destroyed the oil film at this interface and heated the piston up even further.
I do not doubt that in some few cars some cylinder wall scoring has taken place. I suspect it is from a manufacturing defect coupled with a reduction in the amount of time these engines are run at the factory.
In the past this wall scoring would probably have been identified and dealt with at the factory. But now, unfortunately for a few owners, it is they that sometimes find out this has happened.
There can be reasons to limit hard launches with any car including Porches, but piston/cylinder wall scoring is not one of them.
Sincerely,
Rockster.
It seems to me that a third rad should be very high on the mod list for those who can.
I asked my local knowledgeable parts shop today about 5w-50 but they said they'd have to order a crate in. however, they did have Castrol 10w-60, and since sportsandclassic has been using it (even for the gt engine) I think I'll give this a try in the near future.
I would like to have one lot of mods, as I use my car every day so, I shall do all of the cooling mods at once. I'm glad I basically crawl off in first at junctions etc and give the car time to get it together before booting it in second!
I've been considering taking the waterpump out of the loop on my MR2 and replacing it with a temp actuated in-line pump. Would this be of use? That way you could also put the thermostat on the other side of the loop if that would help. It could also increase efficiency as it wouldn't always have to be one. Downsides - having the pump still in place (although the innards could be gutted).
I asked my local knowledgeable parts shop today about 5w-50 but they said they'd have to order a crate in. however, they did have Castrol 10w-60, and since sportsandclassic has been using it (even for the gt engine) I think I'll give this a try in the near future.
I would like to have one lot of mods, as I use my car every day so, I shall do all of the cooling mods at once. I'm glad I basically crawl off in first at junctions etc and give the car time to get it together before booting it in second!
I've been considering taking the waterpump out of the loop on my MR2 and replacing it with a temp actuated in-line pump. Would this be of use? That way you could also put the thermostat on the other side of the loop if that would help. It could also increase efficiency as it wouldn't always have to be one. Downsides - having the pump still in place (although the innards could be gutted).
Edited by coanda on Wednesday 10th August 21:19
Rockster said:
Can't agree with everything you say.
That low temp t-stat may not be the cure all you think it is.
Tests have shown that as the engine temp goes down wear increases and fuel consumption increases.
Here are some numbers:
Temp Wear (cylinder) Fuel Consumption (GPH)
70F 0.008" 3.8
120F 0.002" 3.5
155F 0.001" 3.2
180F 0.0005" 2.9
210F 0.0003" 2.8
Next even though the coolant stream is split into multiple (12) streams and the coolant flows slower each stream is responsible for cooling a smaller region of the engine.
Furthermore, slower coolant speeds in the engine can actually improve cooling as the coolant spends more time flowing past the hotter regions of the engine. These hotter regions are quite small. If the coolant speed is too high the coolant can pass by/over the hotter areas without picking a good load of heat.
Plus it is a common feature in some areas of the coolant passages that coolant nozzles (which are
precision cast into the head) are used which carry coolant from a larger passage to an adjacent but
smaller passage. One end of the nozzle has holes that direct the coolant right at the hottest area
(generally at the exhaust valve seat area). This results in a localized increase in coolant flow speed and circulation which maximizes cooling.
Low coolant speed alone does not result in coolant bubbling (flashing to steam). There has to be
sufficient heat and insufficient pressure for this to happen. My info is that for every one psi increase in cooling system pressure the boiling point of the coolant is raised by 3F. If the system were pressurized to say 15psi the boiling point of the coolant would be raised 45F. The coolant temp could approach 250F and still not boil. At this temp though both radiator fans would be on high speed and would have been at this speed since the coolant temp climbed above 216F or thereabouts.
Next throttle bufferfly valves do not shut immediately. The E-gas controller slows the speed of the
butterfly closure for various reasons: to reduce wear/tear on the butterfly valve shaft/bearings and lower emissions. But this delay in closure means some air flows through the intake and chambers and help remove heat from the combustion chamber and exhaust valves and piston crown.
The engine is spinning at a good clip so coolant flow and oil flow (and oil in most cases is in closer contact with the hotter portions of the engine than coolant) are high so there is considerable cooling taking place.
The oil jets are aimed to spray oil at the underside of the piston. IIRC Porsche has claimed these oil jets reduce piston temps by 50C. This oil can't but help supply extra lubrication -- over and above what the crankshaft/rods sling about -- to the piston/cylinder wall interface.
The oil supply to these jets is controlled by a pressure valve. If the oil pressure drops too low the valve closes to reserve oil pressure and flow for the main bearings. I have to assume the oil pressure though in an otherwise healthy engine and with reasonably fresh oil and of the proper type and SAE viscosity would not have oil pressure dropping so low as to cause this valve to close and cut off oil flow to the piston jets.
Not sure where this belongs but under hard load not only is the piston temp elevated but so is the cylinder's temperature. Sure the cylinder is surrounded by coolant but the cylinder wall's diameter does increase some which helps maintain a suitable clearance between a hot (and larger) piston and the cylinder and its wall in which it resides.
Your scenario of an engine being under high load then going to tickover is a very contrived one. I can't see this happening except in two possible cases: On the track if the driver loses control of the car and ends up in the gravel and avoids engine stall. In this case he is unlikely to move the car off subjecting the engine high loads. The other case could be a driver could make a hard acceleration run then make a sudden stop, perhaps doing a 0mph to 100mph to 0mph test, repeatedly. But car mags which do these tests have not reported any problems with any cars, let alone Porsches.
The T-stat would be quite fully open due to the hotter coolant temp that results from the engine being under high load. These cars are pretty good at keeping themselves cool at road speeds and there are radiator fans which come on if road speed and air flow through the radiators allows the coolant temp to creep up.
My info is the T-stat is located at the output side of the water pump. Cooled coolant flow from the
radiators to the engine is not restricted by the T-stat (at least not directly). The cooling system is filled with fluid so any increase in flow/pressure at the water pump from it spinning up or from the t-stat opening up would result an immediate increase in flow of cooler coolant, coolant that had made its way through a radiator and shed its heat load. Fluid does not compress so a change in pressure at the output side of the water pump/t-stat would be instantly reflected at the coolant inlet of the engine and through the cooling system.
Porsche owners in the UK have it easy with that area's generally mild temps. Here in the USA with generally considerably hotter ambient temps -- how many days have temps been over 100F in some regions of the USA's mid-west region? -- there does not seem to be any significant number of cars (Porsches or any other brands of cars) suffering from the effects of being driven in high temps and I'm sure being subjected to the type of usage you believe can lead to scoring.
If the engine was as weak as you state cylinder wall/piston scoring would be only one result and probably the least severe. Total engine failure would be more likely as the metal to metal contact you suspect is taking place would result not only in scoring (at least at first) but ring and piston failure as the scoring allowed combustion chamber gases (and heat) down along side the piston/cylinder wall which would only exacrebate the problem as this destroyed the oil film at this interface and heated the piston up even further.
I do not doubt that in some few cars some cylinder wall scoring has taken place. I suspect it is from a manufacturing defect coupled with a reduction in the amount of time these engines are run at the factory.
In the past this wall scoring would probably have been identified and dealt with at the factory. But now, unfortunately for a few owners, it is they that sometimes find out this has happened.
There can be reasons to limit hard launches with any car including Porches, but piston/cylinder wall scoring is not one of them.
Sincerely,
Rockster.
I dont doubt your findings and content of your post,however I dont understand how you can can state the bore scoring doesnt apply,I can state it does Ive seen the metal and spoke to the owners on several occasions ,its beyond doubt these engines are (just to mention one know issue!) thermally weak I agree with Baz entirley remember he has a proven repair method and has an increasing pool of cases to refer to and monitor future issues.That low temp t-stat may not be the cure all you think it is.
Tests have shown that as the engine temp goes down wear increases and fuel consumption increases.
Here are some numbers:
Temp Wear (cylinder) Fuel Consumption (GPH)
70F 0.008" 3.8
120F 0.002" 3.5
155F 0.001" 3.2
180F 0.0005" 2.9
210F 0.0003" 2.8
Next even though the coolant stream is split into multiple (12) streams and the coolant flows slower each stream is responsible for cooling a smaller region of the engine.
Furthermore, slower coolant speeds in the engine can actually improve cooling as the coolant spends more time flowing past the hotter regions of the engine. These hotter regions are quite small. If the coolant speed is too high the coolant can pass by/over the hotter areas without picking a good load of heat.
Plus it is a common feature in some areas of the coolant passages that coolant nozzles (which are
precision cast into the head) are used which carry coolant from a larger passage to an adjacent but
smaller passage. One end of the nozzle has holes that direct the coolant right at the hottest area
(generally at the exhaust valve seat area). This results in a localized increase in coolant flow speed and circulation which maximizes cooling.
Low coolant speed alone does not result in coolant bubbling (flashing to steam). There has to be
sufficient heat and insufficient pressure for this to happen. My info is that for every one psi increase in cooling system pressure the boiling point of the coolant is raised by 3F. If the system were pressurized to say 15psi the boiling point of the coolant would be raised 45F. The coolant temp could approach 250F and still not boil. At this temp though both radiator fans would be on high speed and would have been at this speed since the coolant temp climbed above 216F or thereabouts.
Next throttle bufferfly valves do not shut immediately. The E-gas controller slows the speed of the
butterfly closure for various reasons: to reduce wear/tear on the butterfly valve shaft/bearings and lower emissions. But this delay in closure means some air flows through the intake and chambers and help remove heat from the combustion chamber and exhaust valves and piston crown.
The engine is spinning at a good clip so coolant flow and oil flow (and oil in most cases is in closer contact with the hotter portions of the engine than coolant) are high so there is considerable cooling taking place.
The oil jets are aimed to spray oil at the underside of the piston. IIRC Porsche has claimed these oil jets reduce piston temps by 50C. This oil can't but help supply extra lubrication -- over and above what the crankshaft/rods sling about -- to the piston/cylinder wall interface.
The oil supply to these jets is controlled by a pressure valve. If the oil pressure drops too low the valve closes to reserve oil pressure and flow for the main bearings. I have to assume the oil pressure though in an otherwise healthy engine and with reasonably fresh oil and of the proper type and SAE viscosity would not have oil pressure dropping so low as to cause this valve to close and cut off oil flow to the piston jets.
Not sure where this belongs but under hard load not only is the piston temp elevated but so is the cylinder's temperature. Sure the cylinder is surrounded by coolant but the cylinder wall's diameter does increase some which helps maintain a suitable clearance between a hot (and larger) piston and the cylinder and its wall in which it resides.
Your scenario of an engine being under high load then going to tickover is a very contrived one. I can't see this happening except in two possible cases: On the track if the driver loses control of the car and ends up in the gravel and avoids engine stall. In this case he is unlikely to move the car off subjecting the engine high loads. The other case could be a driver could make a hard acceleration run then make a sudden stop, perhaps doing a 0mph to 100mph to 0mph test, repeatedly. But car mags which do these tests have not reported any problems with any cars, let alone Porsches.
The T-stat would be quite fully open due to the hotter coolant temp that results from the engine being under high load. These cars are pretty good at keeping themselves cool at road speeds and there are radiator fans which come on if road speed and air flow through the radiators allows the coolant temp to creep up.
My info is the T-stat is located at the output side of the water pump. Cooled coolant flow from the
radiators to the engine is not restricted by the T-stat (at least not directly). The cooling system is filled with fluid so any increase in flow/pressure at the water pump from it spinning up or from the t-stat opening up would result an immediate increase in flow of cooler coolant, coolant that had made its way through a radiator and shed its heat load. Fluid does not compress so a change in pressure at the output side of the water pump/t-stat would be instantly reflected at the coolant inlet of the engine and through the cooling system.
Porsche owners in the UK have it easy with that area's generally mild temps. Here in the USA with generally considerably hotter ambient temps -- how many days have temps been over 100F in some regions of the USA's mid-west region? -- there does not seem to be any significant number of cars (Porsches or any other brands of cars) suffering from the effects of being driven in high temps and I'm sure being subjected to the type of usage you believe can lead to scoring.
If the engine was as weak as you state cylinder wall/piston scoring would be only one result and probably the least severe. Total engine failure would be more likely as the metal to metal contact you suspect is taking place would result not only in scoring (at least at first) but ring and piston failure as the scoring allowed combustion chamber gases (and heat) down along side the piston/cylinder wall which would only exacrebate the problem as this destroyed the oil film at this interface and heated the piston up even further.
I do not doubt that in some few cars some cylinder wall scoring has taken place. I suspect it is from a manufacturing defect coupled with a reduction in the amount of time these engines are run at the factory.
In the past this wall scoring would probably have been identified and dealt with at the factory. But now, unfortunately for a few owners, it is they that sometimes find out this has happened.
There can be reasons to limit hard launches with any car including Porches, but piston/cylinder wall scoring is not one of them.
Sincerely,
Rockster.
G
Edited by Gary11 on Wednesday 10th August 21:38
Rockster said:
Can't agree with everything you say.
That low temp t-stat may not be the cure all you think it is.
Tests have shown that as the engine temp goes down wear increases and fuel consumption increases.
Here are some numbers:
Temp Wear (cylinder) Fuel Consumption (GPH)
70F 0.008" 3.8
120F 0.002" 3.5
155F 0.001" 3.2
180F 0.0005" 2.9
210F 0.0003" 2.8
Next even though the coolant stream is split into multiple (12) streams and the coolant flows slower each stream is responsible for cooling a smaller region of the engine.
Furthermore, slower coolant speeds in the engine can actually improve cooling as the coolant spends more time flowing past the hotter regions of the engine. These hotter regions are quite small. If the coolant speed is too high the coolant can pass by/over the hotter areas without picking a good load of heat.
Plus it is a common feature in some areas of the coolant passages that coolant nozzles (which are
precision cast into the head) are used which carry coolant from a larger passage to an adjacent but
smaller passage. One end of the nozzle has holes that direct the coolant right at the hottest area
(generally at the exhaust valve seat area). This results in a localized increase in coolant flow speed and circulation which maximizes cooling.
Low coolant speed alone does not result in coolant bubbling (flashing to steam). There has to be
sufficient heat and insufficient pressure for this to happen. My info is that for every one psi increase in cooling system pressure the boiling point of the coolant is raised by 3F. If the system were pressurized to say 15psi the boiling point of the coolant would be raised 45F. The coolant temp could approach 250F and still not boil. At this temp though both radiator fans would be on high speed and would have been at this speed since the coolant temp climbed above 216F or thereabouts.
Next throttle bufferfly valves do not shut immediately. The E-gas controller slows the speed of the
butterfly closure for various reasons: to reduce wear/tear on the butterfly valve shaft/bearings and lower emissions. But this delay in closure means some air flows through the intake and chambers and help remove heat from the combustion chamber and exhaust valves and piston crown.
The engine is spinning at a good clip so coolant flow and oil flow (and oil in most cases is in closer contact with the hotter portions of the engine than coolant) are high so there is considerable cooling taking place.
The oil jets are aimed to spray oil at the underside of the piston. IIRC Porsche has claimed these oil jets reduce piston temps by 50C. This oil can't but help supply extra lubrication -- over and above what the crankshaft/rods sling about -- to the piston/cylinder wall interface.
The oil supply to these jets is controlled by a pressure valve. If the oil pressure drops too low the valve closes to reserve oil pressure and flow for the main bearings. I have to assume the oil pressure though in an otherwise healthy engine and with reasonably fresh oil and of the proper type and SAE viscosity would not have oil pressure dropping so low as to cause this valve to close and cut off oil flow to the piston jets.
Not sure where this belongs but under hard load not only is the piston temp elevated but so is the cylinder's temperature. Sure the cylinder is surrounded by coolant but the cylinder wall's diameter does increase some which helps maintain a suitable clearance between a hot (and larger) piston and the cylinder and its wall in which it resides.
Your scenario of an engine being under high load then going to tickover is a very contrived one. I can't see this happening except in two possible cases: On the track if the driver loses control of the car and ends up in the gravel and avoids engine stall. In this case he is unlikely to move the car off subjecting the engine high loads. The other case could be a driver could make a hard acceleration run then make a sudden stop, perhaps doing a 0mph to 100mph to 0mph test, repeatedly. But car mags which do these tests have not reported any problems with any cars, let alone Porsches.
The T-stat would be quite fully open due to the hotter coolant temp that results from the engine being under high load. These cars are pretty good at keeping themselves cool at road speeds and there are radiator fans which come on if road speed and air flow through the radiators allows the coolant temp to creep up.
My info is the T-stat is located at the output side of the water pump. Cooled coolant flow from the
radiators to the engine is not restricted by the T-stat (at least not directly). The cooling system is filled with fluid so any increase in flow/pressure at the water pump from it spinning up or from the t-stat opening up would result an immediate increase in flow of cooler coolant, coolant that had made its way through a radiator and shed its heat load. Fluid does not compress so a change in pressure at the output side of the water pump/t-stat would be instantly reflected at the coolant inlet of the engine and through the cooling system.
Porsche owners in the UK have it easy with that area's generally mild temps. Here in the USA with generally considerably hotter ambient temps -- how many days have temps been over 100F in some regions of the USA's mid-west region? -- there does not seem to be any significant number of cars (Porsches or any other brands of cars) suffering from the effects of being driven in high temps and I'm sure being subjected to the type of usage you believe can lead to scoring.
If the engine was as weak as you state cylinder wall/piston scoring would be only one result and probably the least severe. Total engine failure would be more likely as the metal to metal contact you suspect is taking place would result not only in scoring (at least at first) but ring and piston failure as the scoring allowed combustion chamber gases (and heat) down along side the piston/cylinder wall which would only exacrebate the problem as this destroyed the oil film at this interface and heated the piston up even further.
I do not doubt that in some few cars some cylinder wall scoring has taken place. I suspect it is from a manufacturing defect coupled with a reduction in the amount of time these engines are run at the factory.
In the past this wall scoring would probably have been identified and dealt with at the factory. But now, unfortunately for a few owners, it is they that sometimes find out this has happened.
There can be reasons to limit hard launches with any car including Porches, but piston/cylinder wall scoring is not one of them.
Sincerely,
Rockster.
That low temp t-stat may not be the cure all you think it is.
Tests have shown that as the engine temp goes down wear increases and fuel consumption increases.
Here are some numbers:
Temp Wear (cylinder) Fuel Consumption (GPH)
70F 0.008" 3.8
120F 0.002" 3.5
155F 0.001" 3.2
180F 0.0005" 2.9
210F 0.0003" 2.8
Next even though the coolant stream is split into multiple (12) streams and the coolant flows slower each stream is responsible for cooling a smaller region of the engine.
Furthermore, slower coolant speeds in the engine can actually improve cooling as the coolant spends more time flowing past the hotter regions of the engine. These hotter regions are quite small. If the coolant speed is too high the coolant can pass by/over the hotter areas without picking a good load of heat.
Plus it is a common feature in some areas of the coolant passages that coolant nozzles (which are
precision cast into the head) are used which carry coolant from a larger passage to an adjacent but
smaller passage. One end of the nozzle has holes that direct the coolant right at the hottest area
(generally at the exhaust valve seat area). This results in a localized increase in coolant flow speed and circulation which maximizes cooling.
Low coolant speed alone does not result in coolant bubbling (flashing to steam). There has to be
sufficient heat and insufficient pressure for this to happen. My info is that for every one psi increase in cooling system pressure the boiling point of the coolant is raised by 3F. If the system were pressurized to say 15psi the boiling point of the coolant would be raised 45F. The coolant temp could approach 250F and still not boil. At this temp though both radiator fans would be on high speed and would have been at this speed since the coolant temp climbed above 216F or thereabouts.
Next throttle bufferfly valves do not shut immediately. The E-gas controller slows the speed of the
butterfly closure for various reasons: to reduce wear/tear on the butterfly valve shaft/bearings and lower emissions. But this delay in closure means some air flows through the intake and chambers and help remove heat from the combustion chamber and exhaust valves and piston crown.
The engine is spinning at a good clip so coolant flow and oil flow (and oil in most cases is in closer contact with the hotter portions of the engine than coolant) are high so there is considerable cooling taking place.
The oil jets are aimed to spray oil at the underside of the piston. IIRC Porsche has claimed these oil jets reduce piston temps by 50C. This oil can't but help supply extra lubrication -- over and above what the crankshaft/rods sling about -- to the piston/cylinder wall interface.
The oil supply to these jets is controlled by a pressure valve. If the oil pressure drops too low the valve closes to reserve oil pressure and flow for the main bearings. I have to assume the oil pressure though in an otherwise healthy engine and with reasonably fresh oil and of the proper type and SAE viscosity would not have oil pressure dropping so low as to cause this valve to close and cut off oil flow to the piston jets.
Not sure where this belongs but under hard load not only is the piston temp elevated but so is the cylinder's temperature. Sure the cylinder is surrounded by coolant but the cylinder wall's diameter does increase some which helps maintain a suitable clearance between a hot (and larger) piston and the cylinder and its wall in which it resides.
Your scenario of an engine being under high load then going to tickover is a very contrived one. I can't see this happening except in two possible cases: On the track if the driver loses control of the car and ends up in the gravel and avoids engine stall. In this case he is unlikely to move the car off subjecting the engine high loads. The other case could be a driver could make a hard acceleration run then make a sudden stop, perhaps doing a 0mph to 100mph to 0mph test, repeatedly. But car mags which do these tests have not reported any problems with any cars, let alone Porsches.
The T-stat would be quite fully open due to the hotter coolant temp that results from the engine being under high load. These cars are pretty good at keeping themselves cool at road speeds and there are radiator fans which come on if road speed and air flow through the radiators allows the coolant temp to creep up.
My info is the T-stat is located at the output side of the water pump. Cooled coolant flow from the
radiators to the engine is not restricted by the T-stat (at least not directly). The cooling system is filled with fluid so any increase in flow/pressure at the water pump from it spinning up or from the t-stat opening up would result an immediate increase in flow of cooler coolant, coolant that had made its way through a radiator and shed its heat load. Fluid does not compress so a change in pressure at the output side of the water pump/t-stat would be instantly reflected at the coolant inlet of the engine and through the cooling system.
Porsche owners in the UK have it easy with that area's generally mild temps. Here in the USA with generally considerably hotter ambient temps -- how many days have temps been over 100F in some regions of the USA's mid-west region? -- there does not seem to be any significant number of cars (Porsches or any other brands of cars) suffering from the effects of being driven in high temps and I'm sure being subjected to the type of usage you believe can lead to scoring.
If the engine was as weak as you state cylinder wall/piston scoring would be only one result and probably the least severe. Total engine failure would be more likely as the metal to metal contact you suspect is taking place would result not only in scoring (at least at first) but ring and piston failure as the scoring allowed combustion chamber gases (and heat) down along side the piston/cylinder wall which would only exacrebate the problem as this destroyed the oil film at this interface and heated the piston up even further.
I do not doubt that in some few cars some cylinder wall scoring has taken place. I suspect it is from a manufacturing defect coupled with a reduction in the amount of time these engines are run at the factory.
In the past this wall scoring would probably have been identified and dealt with at the factory. But now, unfortunately for a few owners, it is they that sometimes find out this has happened.
There can be reasons to limit hard launches with any car including Porches, but piston/cylinder wall scoring is not one of them.
Sincerely,
Rockster.
Rockster, what you say is interesting and informative, but Baz is probably the world's foremost authority on these problems. He dismantles two or three scored and seized engines a week. He's got twenty guys working for him and large engine building rooms and machine shops remanufacturing and fabricating parts for these cars with ten ramps constantly on the go. They have several test cars driving around that they own and they have have been in the business for more than 30 years. People send their cars to Hartech from all over Europe and even some engines from the US. I'll go with what Barry says and I probably will have a low temperature thermostat fitted next time my car's in.
Hi Rockster, sorry I don't know your background but you have managed to put together a load of scientific facts that are basically right and then allowed the conclusion to be the opposite of both common and technical sense and practical experience.
I explained exactly under what circumstances a stop start could occur (you didn't read it all did you?) and even explained why they are OK in racing conditions - so please don't muddy the waters by suggesting otherwise.
What test is it that shows that oil is better at higher temperatures - everyone knows it degrades, is thinner and doesn't do its job as well when engines run too hot - that's why they suffer crankshaft and bore failures when the engines overheat and not when everything is nice and cool.
You correctly confirm what I said that the coolant is going more slowly through the engine - can you not manage to work out that this must mean that it picks up more temperature than if it was going faster and therefore the temperature rise is greater (which is my point). if therefore the thermostat is set higher to start with AND the coolant is going slowly - the output temperature must be much higher and therefore so must the top of the bank 2 cylinder wall.
Out tests showed that the coolant boils under pressure at about 25 to 30 degrees above atmospheric boiling point - but this is anyway not really relevant because if fan speed is higher this cools the coolant in the system more and therefore lowers the entry temperature to the engine through the thermostat. It is impossible to argue against the fact that if the inlet temperature is controlled by a thermostat - AND the amount of cooling to drop the coolant to that temperature (which it does as it is controlled by the coolant flow through the thermostat) then the outlet temperature from the engine simply must be higher. Our tests also showed that although it boils at a higher temperature it starts bubbling much sooner at lower temperatures - largely because of localised heat.
Now lets ask another practical question - what do you do when your baked beans start bubbling in the pan - stir it, what do you do is heating milk starts to boil - stir it, there is no doubt that the slower the coolant speed across the surface the more it is likely to bubble. This is exactly what will happen when you stop for a short while and the engine slows down (and coolant pump) - there can be no argument to support the idea that just then the coolant speeds up - it obviously does not - hence bubbling more likely.
You are also ignoring the fact that the overall temperature of the coolant is the result of it mixing back together from the head and the block - without doing the tests we did - you would not know what temperature the coolant from the block or head is before it mixes back together - I do - and what happens when we stop and start and drive fast etc - because we have tested just that with two cars witted with multiple temperature sensors in the engine and recording on different gauges - Have you done this?
Once a piston has scored it no longer produces the same compression pressure before ignition and therefore runs much cooler - hence the oil temperature at the surface of the piston to cylinder wall interface is actually lower and the rings have less to do.
Your comments that scoring just doesn't actually happen makes me wonder if you are working for Porsche under instruction to mix a load of technical rights with a load of nonsense conclusions to dilute the truth from being established. You seem to be living in a theoretical dream world in which you can persuade yourself that reality doesn't exist if your technical knowledge suggests to you it is impossible - but without practical experience and tests your conclusions are anyway totally flawed. Your posting seems to me to be from an academic with little practical experience and it is only that practical hands on work combined with technical knowledge that enables engineers to work out how they fit together and what actually happens inside the engine.
Your last sentence is in all honesty disgraceful and I hope you are never confronted by the hundreds of owners faced with a financial disaster because they expected a Porsche to be better engineered than it obviously is - or for the manufacturers to do something to help them when faced with an obvious technical design shortcoming.
I suppose at least you have managed to manipulate me to spending more time defending my advice than providing more (perhaps that was the aim and I fell for it) so at risk of allowing more similar nonsense to be posted and the resulting confusion from limiting the public's understanding - I am going to ignore your further posts and concentrate on advising those that can see through these and similar posts (and I am grateful to those supporting me with similar common sense practical points and experiences that prove that these engines have a bore scoring problem).
I am still not sure why anyone would be motivated to discredit advice intended to help avoid damage - that can do no harm whatsoever to the car and could only help - unless there are more sinister motives - or they are the rantings of someone who has no practical experience and cannot bear to see someone else appearing to know the score and hold a place on the internet as an expert.
I find it very sad that someone so obviously knowledgeable can spend so long discrediting someone with proven knowledge, experience and who is fully technically qualified, who has out-designed the might of the Japanese motorcycle industry and who clearly has resolved many of the existing problems and is simply offering some advice that might help. Presumably you prefer people to thrash their cars immediately after being forced to sit stationary for a while (because you think that could not cause scoring) rather than consider that there might be some good reasoning in my advice (combined with actual practical road tests and temperature readings) and therefore - as no harm could possibly be dome by my suggestions - just keep out of it.
Baz
I explained exactly under what circumstances a stop start could occur (you didn't read it all did you?) and even explained why they are OK in racing conditions - so please don't muddy the waters by suggesting otherwise.
What test is it that shows that oil is better at higher temperatures - everyone knows it degrades, is thinner and doesn't do its job as well when engines run too hot - that's why they suffer crankshaft and bore failures when the engines overheat and not when everything is nice and cool.
You correctly confirm what I said that the coolant is going more slowly through the engine - can you not manage to work out that this must mean that it picks up more temperature than if it was going faster and therefore the temperature rise is greater (which is my point). if therefore the thermostat is set higher to start with AND the coolant is going slowly - the output temperature must be much higher and therefore so must the top of the bank 2 cylinder wall.
Out tests showed that the coolant boils under pressure at about 25 to 30 degrees above atmospheric boiling point - but this is anyway not really relevant because if fan speed is higher this cools the coolant in the system more and therefore lowers the entry temperature to the engine through the thermostat. It is impossible to argue against the fact that if the inlet temperature is controlled by a thermostat - AND the amount of cooling to drop the coolant to that temperature (which it does as it is controlled by the coolant flow through the thermostat) then the outlet temperature from the engine simply must be higher. Our tests also showed that although it boils at a higher temperature it starts bubbling much sooner at lower temperatures - largely because of localised heat.
Now lets ask another practical question - what do you do when your baked beans start bubbling in the pan - stir it, what do you do is heating milk starts to boil - stir it, there is no doubt that the slower the coolant speed across the surface the more it is likely to bubble. This is exactly what will happen when you stop for a short while and the engine slows down (and coolant pump) - there can be no argument to support the idea that just then the coolant speeds up - it obviously does not - hence bubbling more likely.
You are also ignoring the fact that the overall temperature of the coolant is the result of it mixing back together from the head and the block - without doing the tests we did - you would not know what temperature the coolant from the block or head is before it mixes back together - I do - and what happens when we stop and start and drive fast etc - because we have tested just that with two cars witted with multiple temperature sensors in the engine and recording on different gauges - Have you done this?
Once a piston has scored it no longer produces the same compression pressure before ignition and therefore runs much cooler - hence the oil temperature at the surface of the piston to cylinder wall interface is actually lower and the rings have less to do.
Your comments that scoring just doesn't actually happen makes me wonder if you are working for Porsche under instruction to mix a load of technical rights with a load of nonsense conclusions to dilute the truth from being established. You seem to be living in a theoretical dream world in which you can persuade yourself that reality doesn't exist if your technical knowledge suggests to you it is impossible - but without practical experience and tests your conclusions are anyway totally flawed. Your posting seems to me to be from an academic with little practical experience and it is only that practical hands on work combined with technical knowledge that enables engineers to work out how they fit together and what actually happens inside the engine.
Your last sentence is in all honesty disgraceful and I hope you are never confronted by the hundreds of owners faced with a financial disaster because they expected a Porsche to be better engineered than it obviously is - or for the manufacturers to do something to help them when faced with an obvious technical design shortcoming.
I suppose at least you have managed to manipulate me to spending more time defending my advice than providing more (perhaps that was the aim and I fell for it) so at risk of allowing more similar nonsense to be posted and the resulting confusion from limiting the public's understanding - I am going to ignore your further posts and concentrate on advising those that can see through these and similar posts (and I am grateful to those supporting me with similar common sense practical points and experiences that prove that these engines have a bore scoring problem).
I am still not sure why anyone would be motivated to discredit advice intended to help avoid damage - that can do no harm whatsoever to the car and could only help - unless there are more sinister motives - or they are the rantings of someone who has no practical experience and cannot bear to see someone else appearing to know the score and hold a place on the internet as an expert.
I find it very sad that someone so obviously knowledgeable can spend so long discrediting someone with proven knowledge, experience and who is fully technically qualified, who has out-designed the might of the Japanese motorcycle industry and who clearly has resolved many of the existing problems and is simply offering some advice that might help. Presumably you prefer people to thrash their cars immediately after being forced to sit stationary for a while (because you think that could not cause scoring) rather than consider that there might be some good reasoning in my advice (combined with actual practical road tests and temperature readings) and therefore - as no harm could possibly be dome by my suggestions - just keep out of it.
Baz
Rockster I appreciate your response but I'm with Baz. Unless you can prove your technical theories, having actually gotten your hands dirty and having had Baz's experience with these engines then I'm sorry I believe you are a Porsche Head Office Stooly. You always seem to oppose what Baz has to say. Baz food for thought eh ?.
Not sure why anyone would want to argue the toss against Baz, no one can possibly know more about the problems these engines suffer from. What has he got to gain by giving this advice. If everyone listens to Baz he will lose out on business as there will be less scored cylinders. This shows that he is genuinely interested in helping us. Lets face it, if our car is out of Porsche warranty and suffers an engine problem who are we going to trust to rebuild it???
I am in no way technically experienced with engine problems and am not in the profession,
can I ask a question as a person from a basic viewpoint.
With the water cooled rear engined porsches, what effect does the radiators being far away from the engines have? I assume they are at the front?
also do the 997 engines suffer from the same problems? are they a revision on the 996 engine or a new design, if it is a revision and it doesn't have the same issues, what have porsche changed?
can I ask a question as a person from a basic viewpoint.
With the water cooled rear engined porsches, what effect does the radiators being far away from the engines have? I assume they are at the front?
also do the 997 engines suffer from the same problems? are they a revision on the 996 engine or a new design, if it is a revision and it doesn't have the same issues, what have porsche changed?
hartech said:
It is therefore clear that when the scoring occurs – one side of the piston is sufficiently cool to lubricate the piston/bore face and support the piston whereas the other side has become excessively hot and the oil film cannot support the loads applied – which result in metal to metal contact – overheating of the surface and scoring the bores and piston on one side only.
This makes sense. The oil is shearing to 'nothing' under excessive heat in a specific area of the bore. So it is logical to look at the nature of cooling in that area, which is evidently problematic by design.If I had a 997 M97 I'd be running higher temp oil, and driving sympathetically as a precaution.
BMW had very similar issues with their M motors and now the manufacturer insists on 10w60. It is odd that Porsche are seemingly silent - difficult for them to admit their failing I would guess. I wonder how they dealt with the myriad of teething problems with the air-cooled engine that took decades to perfect?
And is Mobil1 0w40 what it used to be.. I wonder.
anonymous said:
[redacted]
It is quite possible. An efficient cooling system should be thermally loading the coolant media as high as possible, whilst reserving some capacity for use during times of high demand. The overhead capacity is an estimation made by the engineering team, having considered all the analysis available to them. Unfortunately, one of the first things you learn as a real world engineer designing complex machines is that all the tools you use (including actual test) are only an approximation of the real world. Some of the tools, methods, graphs, software etc are more of an approximation than others. Fluid Dynamics, along with FEA are, perhaps most susceptible to providing results that could be complete and utter tosh. And that's with todays technology. When were these engines designed? 1996? Thats an ice age ago in computing power and software capability. Of course, the key to useable results is to have a user that can apply his/her engineering bulls
t filter to computer output to check whether the output is trash or not. This goes for bolted joints, to the flexure of airliner wings, to the airflow over those wings, to the internal flow of coolant in an engine.With the coolant system, an immediate and high demand will transfer heat through the cylinder walls fast (because the metal is already at a high average temperature, is thin, and transmits heat fast anyway) and move into the coolant adjacent to the cylinder walls, then it will have to propagate through the coolant media itself.
I think it reasonable to say that the coolant media will only work under a certain temperature range for a given system pressure, and that range is far below that of the temperatures inside the cylinder during ignition (which I assume are highest for a max torque condition). The extra instantaneous heat load will, for a short time, exceed the thermal capacity of coolant local to the cylinder wall. The coolant at or near the cylinder wall will be slower (actually pretty much zero as it is the natural boundary layer) than the 'free stream' coolant flow within the engine, which itself, will be slower than the coolant flow around the rest of the cooling system. The actual time of occurence for these very high temp situations may only be relatively small, but, the overhead capacity of the coolant may only be 1 or 2 degrees local to the cylinder wall, so the cylinder walls would only need to transfer a small percent of the gas temp to cause trouble for the coolant. The real killer comes when the coolant adjacent to the cylinder wall bubbles up and effectively forms an air gap around the cylinder. Air is an excellent insulator, leading to heat being retained within the cylinder walls. As I understand it, the cylinder will then expand - which means the outer wall will move away from the centre of the cylinder, but the inner wall will move towards the centre of the cylinder, even if by a tiny amount.
This can all go on within the engine and the operator may never see it because the coolant system has volume, and the extra heat will take time to propogate through the system. The 'overheated' coolant volume may only be a very small proportion of the total system volume so the average temperature rise when the 'overheated' coolant is finally thoroughly distributed through the system will be small. Yes, the coolant is moving, but it still takes time, and that time period is longer (probably much longer) than the high temp ignition period.
On a 'global' scale, there isn't much to see, but on a 'local' scale you had a short term overheat condition.
In terms of driving conditions, I can see when I have to do stop-start town/traffic driving, or nipping from roundabout to roundabout that my temperature gauge creeps up. As we now know, this gauge isn't providing us with the max temp in the system, so coolant temps will be even higher in some places. It seems the effective way to reduce those temps is to get the waterpump speed up and increase radiator air flow. You've got to get the car to speed carefully and drive it faster!
I wonder whether this might be a case of lagging the engine (say accelerating from 25mph in 6th) just as much as frequent low road speed speed/high rev situations because the high revs would at least have the water pump working faster.
I looked for a heat transfer example that might be applicable here so we could see just how fast energy is transferred from a hot gas, though a hot wall, to a coolant media, but it gets complex quick just for simple overall heat transfer coefficients. I'll keep looking.
I don't think I follow you on that one cmoose?
I don't have need for this in aerostructures, so I had to go and look it up again.
I don't think this link agrees with you?
http://www.brighthub.com/engineering/mechanical/ar...
I don't have need for this in aerostructures, so I had to go and look it up again.
I don't think this link agrees with you?
http://www.brighthub.com/engineering/mechanical/ar...
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