996-997 wet-sump engine reliability: enter your stats here!
Discussion
In June 2009 I bought a 2002 996 70,000 mls,when I picked it up it smoked a little from the left hand side I was told that was because it had been sitting at an angle in the showroom two months later it developed a tick.After ongoing
alternatives ie;different vehicles etc I am pleased to say that the car is now at Hartech and the engine is being rebuilt with what I believe to be six pistons and support rings and an assortment of cylinders,3 pistons and cylinders to cure the fault and the rest preventative.
Looking forward to getting the rest of the car into the condition it should be in as through the winter I have used it non stop what a fantastic motor it was in the snow as it`s a carrera 4 totally amazed all the 4x4 owners here.(Comrie,Perthshire)never stuck....
alternatives ie;different vehicles etc I am pleased to say that the car is now at Hartech and the engine is being rebuilt with what I believe to be six pistons and support rings and an assortment of cylinders,3 pistons and cylinders to cure the fault and the rest preventative.
Looking forward to getting the rest of the car into the condition it should be in as through the winter I have used it non stop what a fantastic motor it was in the snow as it`s a carrera 4 totally amazed all the 4x4 owners here.(Comrie,Perthshire)never stuck....
For those of you interested in the various cylinder scoring problems emerging of a few 3.6 and 3.8 engines - I have been driving with the dashboard air-con screen set to read actual digital coolant temperature (as previously reported) and have found not only does the normal analogue temperature dial read low after about 84 degrees - but it also shows the effect of low revs and the coolant temperature (as I proposed was a contributory factore some weeks ago).
As I am driving a tiptronic in auto mode - in traffic it revs very low and often the temperature rises (even in UK winter) to 95 to 98 on the digital read out (still 84 to 86 on the normal guage), then when I drive away from say a restriction and can drive a little faster the temperature is very slow to fall unless I put it into tiptronic mode and flick down the gearbox to increase engine (and hence water pump)speed (but no increase in engine heat generation as the same power output).
Watching the normal guage doesn't show this because it is slow to move and doesn't record properly over 84 degrees so any rise is reduced on that guage anyway - but watching the digital readout shows fast responses and does seem to confirm that the long passage for the coolant combined with low engine revs takes a longer time to recover a high cylinder temperature than if the engine was revved higher and this is what I suspected was a contributory factor in the much more torquey 3.6 and 3.8 engine driving experiences and failures.
Baz
As I am driving a tiptronic in auto mode - in traffic it revs very low and often the temperature rises (even in UK winter) to 95 to 98 on the digital read out (still 84 to 86 on the normal guage), then when I drive away from say a restriction and can drive a little faster the temperature is very slow to fall unless I put it into tiptronic mode and flick down the gearbox to increase engine (and hence water pump)speed (but no increase in engine heat generation as the same power output).
Watching the normal guage doesn't show this because it is slow to move and doesn't record properly over 84 degrees so any rise is reduced on that guage anyway - but watching the digital readout shows fast responses and does seem to confirm that the long passage for the coolant combined with low engine revs takes a longer time to recover a high cylinder temperature than if the engine was revved higher and this is what I suspected was a contributory factor in the much more torquey 3.6 and 3.8 engine driving experiences and failures.
Baz
I owned a 2000 996 3.4 cab for three years without a problem, did 10K mile a year in it, services regularly. car had 42K miles when i chopped it in.
Then a 2002 996 turbo for 4 years, never missed a beat, did about 20K miles during ownership, serviced every year, never missed a beat. car had 40K miles when i sold it.
I took a Porsche warranty with the first car as there was a lot of talk of bore liners slipping and ending in failure, didn't bother with the turbo as the cost was stupid.
Then a 2002 996 turbo for 4 years, never missed a beat, did about 20K miles during ownership, serviced every year, never missed a beat. car had 40K miles when i sold it.
I took a Porsche warranty with the first car as there was a lot of talk of bore liners slipping and ending in failure, didn't bother with the turbo as the cost was stupid.
The turbo engine is a different design BTW, unburstable with a decent timing chain and water pump IIRC.
Baz can I ask a quick question?
If I had a 987 Boxster or Boxster S what sort of money would be needed to rebuild an old but working engine to your standards (ideally one for a turnkey 'here's the car' and one for a 'here's the engine' cost?). How much would it jump if the engine was blown already?
The reason I'm asking is that if I do get a cheap 987 one day I'd like to price in an 'engine strengthening' exercise to allow me to use it properly and be able to depend on it. I'm not after an accurate price - just ballpark!
Baz can I ask a quick question?
If I had a 987 Boxster or Boxster S what sort of money would be needed to rebuild an old but working engine to your standards (ideally one for a turnkey 'here's the car' and one for a 'here's the engine' cost?). How much would it jump if the engine was blown already?
The reason I'm asking is that if I do get a cheap 987 one day I'd like to price in an 'engine strengthening' exercise to allow me to use it properly and be able to depend on it. I'm not after an accurate price - just ballpark!
hartech said:
Perhaps you could pop over for a chat about it all - rather than deal with it over the Internet then?
Again - today - another clue as to why we try to do things the right way. An enquiry from a Cayman owner whose car was seen to have scored bores in another dealer (linked with Porsche) and they wanted a huge amount of money to strip it down to see if they could then apply for a gesture from Porsche towards the cost of fixing it (and we already know that outcome).
This reafirms our advice to get any car suspected of problems here first because that would have ended up being unecconomic to bring to us after that payment and they - like us - already know only too well exactly what they will find inside (and if they really cannot they ought to be able to!).
If you pop over I can show you the sumps in production and explain why the others on the market actually don't do the job properly and we can cover several other issues and get you set up as soon as possible.
Baz
Hi Baz,Again - today - another clue as to why we try to do things the right way. An enquiry from a Cayman owner whose car was seen to have scored bores in another dealer (linked with Porsche) and they wanted a huge amount of money to strip it down to see if they could then apply for a gesture from Porsche towards the cost of fixing it (and we already know that outcome).
This reafirms our advice to get any car suspected of problems here first because that would have ended up being unecconomic to bring to us after that payment and they - like us - already know only too well exactly what they will find inside (and if they really cannot they ought to be able to!).
If you pop over I can show you the sumps in production and explain why the others on the market actually don't do the job properly and we can cover several other issues and get you set up as soon as possible.
Baz
In the above case the goodwill aspect was affected by a non-OPC service stamp and a non-genuine sports exhaust; warranty are understandably very critical in this area (photos and evidence files are a prerequisite now). I have no doubt that a goodwill claim would have been succesful if the circumstances were different.
The fault was easily diagnosed with the minimum of time (sooty exhaust/plugs fouled and boroscope check revealing piston seizure) our directions at that point are to ascertain the most economical repair (repair v replace) and a strip is the only way to get to this end.
Regarding the coolant temp sensor readings in your latest post; the sensor signal is used by the Instrument Cluster to provide a reading (within a range) to give the driver the impression (and therein peace of mind) that the engine is maintaining a steady temperature regardless of use once up to temperature, though I see your points (unsympathetic use in the warm-up phase causing localised heating and subsequent damage and oil film breakdown due to increased loading) if a correct warm-up procedure was rigidly adhered to would the issue be as prevalent?
I do not wish to cause any offence (mindful of our previous history) and respect your efforts in this area. Unfortunately (for me) where you have the freedom to experiment and improve - if I wish to remain in employment where I do my hands are tied.
Hi Baz,
I recently bought a 1998 C2 996 Auto with 40,000 on the clock. The car runs like a dream except between 3000 and 5000 revs there is a rattle that appears to come from the automatic gear shift. It makes this vibrating rattling sound in every gear between those revs and by squeezing the loose plastic at the base of the shift and the button it seems to stop slightly. It doesn’t make this noise when revving in neutral, only when in gear. Any advise as to what this may be - could it be the death rattle from a wobbly shaft?
Cheers Alex
I recently bought a 1998 C2 996 Auto with 40,000 on the clock. The car runs like a dream except between 3000 and 5000 revs there is a rattle that appears to come from the automatic gear shift. It makes this vibrating rattling sound in every gear between those revs and by squeezing the loose plastic at the base of the shift and the button it seems to stop slightly. It doesn’t make this noise when revving in neutral, only when in gear. Any advise as to what this may be - could it be the death rattle from a wobbly shaft?
Cheers Alex
Back in the UK now and responses follow.
Globs - the 987's and Boxster S versions are the most reliable probably mainly only having IMS bearing issues.
Prices for rebuilds depend on many factors. (1) transport to us (free if you drive it here of course), (2) if we take the whole car or just the engine, (3) what is wong with it that must be fixed, (4) what else the customer might like doing at the same time to improve it etc.
To help we operate a fixed price start point that covers strip, inspection, measuring, cleaning and rebuilding with new gaskets, seals oil and coolant, road testing etc and then add to that what the essential repair cost is and what else the customers wants doing to future proof the engine.
Our current prices are as follows:-
Whole car already here £3500 + Vat Fully guaranteed.
Engine with anciliaries removed £2200 + Vat engine work guaranteed.
Our guarantee is quite simple and fair - if we recomend something that we feel needs replacing and the customer declines and the engine then fails through that part - we may - in all fairness - decline cover (although we would try and help anyway). If we only built the engine and a fault related to how it was fitted etc - then again the same answer applies.
However we have built so many engines for so many years (many of which were in a terrible state) without any problems or claims - I would not worry about it too much and apart from anything else this is becoming a major part of our future business (in which we have and are investing heavily) which we would not prejudice if customers are reasonable.
Typical costs to add for the faults etc are as follows:- IMS bearing mods - £150 + vat, New Shells, £110 + Vat, New Chains £208 + Vat - but we need to see inside before we can finalise our advice and customers decide what they want. Usually this depends on how long they intend to keep the car.
Pope - Thanks - i understand why the temp guages work as they do but it is unfortunate that this delayed our diagnosis (although we correctly suspected temperatures were too high from deducing what the difference was between the earlier models without the scoring issues and the later ones with it) until we put our own guages on the cars after which we began to understand what the causes are.
I agree with you that it would be better if warm up proceedures were dutifully followed (but that is never going to be certain with some owners) but the overall problem is (IMHO) due to basic temperatures running too high for the "inertia" of the cooling system to catch up in time - and this would still happen going from modest to aggressive driving in a short time span - even if the engine was fully warmed up initially.
Your contributions have always seemed to me to be valuable and accurate and I certainly appreciate your position and your subtle and diplomatic way of explaining why your comments must be slanted in one direction (although they are always valuable to me and I am sure others).
Alexstrella - I am sorry but I have decided not to try and comment too much on other peoples description of noises - it is just too open to missinterpretation and really it needs a specialist to hear them directly to value the answers that may otherwise mislead.
There is however a particular noise issue with some engines that we have been struggling to identify. We have changed so many parts to eliminate it without success (and at huge cost) that we have had to consider alternative explanations.
It sounds like piston slap or a tappet or chain tensioner - but on revving the engine and changing the tickover revs - doesn't respond as you would expect for those problems. It seems prevelant on tiptronics much more than manuals and is always on the back end of the bank 2 (unfortunately the same area as most 3.6, 3.8 and Caymen pistons score bores and they DO piston slap) - but is not caused by that. I now think it is caused by the same thing that affects race engines with light flywheels - whereby the crankshaft fluctuations are insufficiently damped by the mass of the system at low revs and cause backlash snatch through the cam chain system. A similar cause afflicts 996 turbo IMS gears, GT3's generally and can also be heard as gearbox scrawl in older 3.2 911's etc. I think that the extra chain in the bank 1 end splashes more oil about at that end but with only one chain on the bank 2 cam drive end - at tickover - there is less oil splashed onto the chains and sprockets at tickover and that a tiptronic effectively has a lighter flywheel when it is not driving the torque converter and the system picks up the snatch resulting (although a worn dual mass flywheel may well have the same result). This explains why - on testing - if you rev the engine it is oK and then when it returns to tickover the noise gradually appears after a few seconds - as we think - the oil that was damping the chain drive system gradually squeezes out of the chain and sprockets until the revs rise again.
This is quite important as it may well be practically impossible to get rid of (without extensive and uneccessary replacement parts) and probably can be ignored unless it is a sign of an iminent IMS failure, a scored bore, or indeed a tappet etc - and is not easy to differentiate between the options.
I hope this catches me up to date with responses. If I have missed anything please let me know.
Baz
Globs - the 987's and Boxster S versions are the most reliable probably mainly only having IMS bearing issues.
Prices for rebuilds depend on many factors. (1) transport to us (free if you drive it here of course), (2) if we take the whole car or just the engine, (3) what is wong with it that must be fixed, (4) what else the customer might like doing at the same time to improve it etc.
To help we operate a fixed price start point that covers strip, inspection, measuring, cleaning and rebuilding with new gaskets, seals oil and coolant, road testing etc and then add to that what the essential repair cost is and what else the customers wants doing to future proof the engine.
Our current prices are as follows:-
Whole car already here £3500 + Vat Fully guaranteed.
Engine with anciliaries removed £2200 + Vat engine work guaranteed.
Our guarantee is quite simple and fair - if we recomend something that we feel needs replacing and the customer declines and the engine then fails through that part - we may - in all fairness - decline cover (although we would try and help anyway). If we only built the engine and a fault related to how it was fitted etc - then again the same answer applies.
However we have built so many engines for so many years (many of which were in a terrible state) without any problems or claims - I would not worry about it too much and apart from anything else this is becoming a major part of our future business (in which we have and are investing heavily) which we would not prejudice if customers are reasonable.
Typical costs to add for the faults etc are as follows:- IMS bearing mods - £150 + vat, New Shells, £110 + Vat, New Chains £208 + Vat - but we need to see inside before we can finalise our advice and customers decide what they want. Usually this depends on how long they intend to keep the car.
Pope - Thanks - i understand why the temp guages work as they do but it is unfortunate that this delayed our diagnosis (although we correctly suspected temperatures were too high from deducing what the difference was between the earlier models without the scoring issues and the later ones with it) until we put our own guages on the cars after which we began to understand what the causes are.
I agree with you that it would be better if warm up proceedures were dutifully followed (but that is never going to be certain with some owners) but the overall problem is (IMHO) due to basic temperatures running too high for the "inertia" of the cooling system to catch up in time - and this would still happen going from modest to aggressive driving in a short time span - even if the engine was fully warmed up initially.
Your contributions have always seemed to me to be valuable and accurate and I certainly appreciate your position and your subtle and diplomatic way of explaining why your comments must be slanted in one direction (although they are always valuable to me and I am sure others).
Alexstrella - I am sorry but I have decided not to try and comment too much on other peoples description of noises - it is just too open to missinterpretation and really it needs a specialist to hear them directly to value the answers that may otherwise mislead.
There is however a particular noise issue with some engines that we have been struggling to identify. We have changed so many parts to eliminate it without success (and at huge cost) that we have had to consider alternative explanations.
It sounds like piston slap or a tappet or chain tensioner - but on revving the engine and changing the tickover revs - doesn't respond as you would expect for those problems. It seems prevelant on tiptronics much more than manuals and is always on the back end of the bank 2 (unfortunately the same area as most 3.6, 3.8 and Caymen pistons score bores and they DO piston slap) - but is not caused by that. I now think it is caused by the same thing that affects race engines with light flywheels - whereby the crankshaft fluctuations are insufficiently damped by the mass of the system at low revs and cause backlash snatch through the cam chain system. A similar cause afflicts 996 turbo IMS gears, GT3's generally and can also be heard as gearbox scrawl in older 3.2 911's etc. I think that the extra chain in the bank 1 end splashes more oil about at that end but with only one chain on the bank 2 cam drive end - at tickover - there is less oil splashed onto the chains and sprockets at tickover and that a tiptronic effectively has a lighter flywheel when it is not driving the torque converter and the system picks up the snatch resulting (although a worn dual mass flywheel may well have the same result). This explains why - on testing - if you rev the engine it is oK and then when it returns to tickover the noise gradually appears after a few seconds - as we think - the oil that was damping the chain drive system gradually squeezes out of the chain and sprockets until the revs rise again.
This is quite important as it may well be practically impossible to get rid of (without extensive and uneccessary replacement parts) and probably can be ignored unless it is a sign of an iminent IMS failure, a scored bore, or indeed a tappet etc - and is not easy to differentiate between the options.
I hope this catches me up to date with responses. If I have missed anything please let me know.
Baz
I think I now have the shopping list for my 996 on this one!!!
1 The lower temp engine thermostat.
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, with temperature monitor in the cabin and adjustable cut-in temperature. Obviously as a failsafe the pump should not stop any flow when off. No idea how to achieve all this -at the moment but pumps exist on ebay and PC components come to mind for the controller!
3 A non return flap/valve in the large diameter front-rear cooling pipework to prevent the flow reversing on acceleration or braking. Could be hard to figure a good design for this.
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 -GT4:any idea how existing settings can be mofified for this (without aircon on)?
5 Modified front wheel arch liners so permit some actual darned air flow through the front radiators at low driving speeds !!! ie fixing the design error. Will do this soon and will probably copy the GT3 cut-out design.
6 A reduction in the temperature at which the engine bay fans start up, yes; adjustable! and maybe with post engine-off delay timer (lower speed). Dont know why I want this, just dont like the idea of the lump and all its exhaust systems sitting there cooking as I walk away from it!!!
Any more...?
1 The lower temp engine thermostat.
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, with temperature monitor in the cabin and adjustable cut-in temperature. Obviously as a failsafe the pump should not stop any flow when off. No idea how to achieve all this -at the moment but pumps exist on ebay and PC components come to mind for the controller!
3 A non return flap/valve in the large diameter front-rear cooling pipework to prevent the flow reversing on acceleration or braking. Could be hard to figure a good design for this.
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 -GT4:any idea how existing settings can be mofified for this (without aircon on)?
5 Modified front wheel arch liners so permit some actual darned air flow through the front radiators at low driving speeds !!! ie fixing the design error. Will do this soon and will probably copy the GT3 cut-out design.
6 A reduction in the temperature at which the engine bay fans start up, yes; adjustable! and maybe with post engine-off delay timer (lower speed). Dont know why I want this, just dont like the idea of the lump and all its exhaust systems sitting there cooking as I walk away from it!!!
Any more...?
911Fiddler said:
I think I now have the shopping list for my 996 on this one!!!
1 The lower temp engine thermostat.
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, with temperature monitor in the cabin and adjustable cut-in temperature. Obviously as a failsafe the pump should not stop any flow when off. No idea how to achieve all this -at the moment but pumps exist on ebay and PC components come to mind for the controller!
3 A non return flap/valve in the large diameter front-rear cooling pipework to prevent the flow reversing on acceleration or braking. Could be hard to figure a good design for this.
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 -GT4:any idea how existing settings can be mofified for this (without aircon on)?
5 Modified front wheel arch liners so permit some actual darned air flow through the front radiators at low driving speeds !!! ie fixing the design error. Will do this soon and will probably copy the GT3 cut-out design.
6 A reduction in the temperature at which the engine bay fans start up, yes; adjustable! and maybe with post engine-off delay timer (lower speed). Dont know why I want this, just dont like the idea of the lump and all its exhaust systems sitting there cooking as I walk away from it!!!
Any more...?
Your mods sound interesting but perhaps do not address the essential element of a faster cylinder cooling flow required, which I suspect at least requires new head gaskets and possibly some machining.1 The lower temp engine thermostat.
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, with temperature monitor in the cabin and adjustable cut-in temperature. Obviously as a failsafe the pump should not stop any flow when off. No idea how to achieve all this -at the moment but pumps exist on ebay and PC components come to mind for the controller!
3 A non return flap/valve in the large diameter front-rear cooling pipework to prevent the flow reversing on acceleration or braking. Could be hard to figure a good design for this.
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 -GT4:any idea how existing settings can be mofified for this (without aircon on)?
5 Modified front wheel arch liners so permit some actual darned air flow through the front radiators at low driving speeds !!! ie fixing the design error. Will do this soon and will probably copy the GT3 cut-out design.
6 A reduction in the temperature at which the engine bay fans start up, yes; adjustable! and maybe with post engine-off delay timer (lower speed). Dont know why I want this, just dont like the idea of the lump and all its exhaust systems sitting there cooking as I walk away from it!!!
Any more...?
Hartech: Thanks for the info, useful ballpark figures I'll keep in mind, and you'll know when I finally make it into a 987
. Sounds like a pre-blowup engine rebuild is the way to go - I'd rather schedule a pit-stop than be stranded on holiday wishing I'd had it done before!! Globs and 911 fiddler - thanks for those posts - it is encourasging to see that some readers understand the issues I have been trying to describe - correctly.
The 986's seem OK and also the early 996's so 2.5, 2.7, 3.2, and 3.4 996 - all seem OK because they have head gaskets that allow more coolant flow through the blocks and less torque (hence less pressure squeezing the piston against the thrust side of the cylinder wall at low revs when the water pump is not delivering full flow). Smaller than 3.4 do not have coated pistons and nor do the early 3.4's but later ones do but seem also to be OK.
It is only (so far) the 3.4 Cayman, 3.6 and 3.8 engines that all have coated pistons, common head gaskets (that reduce flow through the block) and have not increased the flow through the block any other way - so have not increased the coolant flow control slots in line with the increases in power and torque and therefore have to run with that higher squeezing load of the piston to cylinder wall.
It seems that those driven modestly eventually wear away the coating but may continue to run OK or eventually "pick up" damage on the piston face and bore while those driven more aggresively seem to have the coating flake off and jam under the oil control rings - eventually dragging a score down the bore before the piece of coating slides out (I will post some pictures soon to demonstrate the differences).
All the ideas to improve coolant and air flow rates are good but if the thermostat is set at a high temperature before opening - then whatever you do it will restrict the coolant flow by not opening enough to benefit - so the engine will still be running at a high temperature and then when a fast drive is needed - the inertia of the cooling system will still take time to react and probably would not be fast enough to prevent damage since the start temperature will still be too high. So a lower temperature thermostat - is to my mind a must and the first priority - is simple to supply - a bit difficult to fit but by no means as difficult as any other suggestions and can be fitted Worldwide.
Better still when we rebuild engines to increase the flow rate to the cylinders (as we do) but the radiator fan control temperature is not as high on the priority list because a low temperature thermostat means that when spirited driving is used - the start temperature of the system will already be a lot lower than it used to be so by the time the coolant temperature rises - the thermostat opens some more and the cooling kicks in the engine has not risen more than it used to run at all the time normally anyway.
It is true that if you were stuck in a queue then the temperature might rise to 100 or so but then the lower temperature thermostat would be fully open and respond quickly to allow full flow as soon as you drive off and the revs rise whereas even the std thermostat may not be fully open and would soon start closing again - as it works at a higher range.
I cannot guess how much longer a low temperature thermostat will make the engines (that have already run and may already be damaged) - last - but it could and should prevent or delay potential damage.
My biggest concern is that the engines we have rebuilt have been praised for running better than they ever have - suggesting that the previous owner may have been running with some scoring that gradually got worse for some time. This view is reinforced by the high proportion of engines we are checking with a boroscope (before accepting them on our Maintenance Plan) that already have some scratches and damage but show no sign of it in oil consumption or running yet.
I fear therefore that these engines will fail at lower mileages and more numbers than the previous 3.4 996's did (hence our huge investment in repairing them that will take several years to recover).
Hence our best advice to fit a low temperature thermostat as soon as possible and avoid dramatic changes in load - instead building up to a fast full throttle driving speed over a longer period of perhaps 20 or 30 seconds.
Baz
The 986's seem OK and also the early 996's so 2.5, 2.7, 3.2, and 3.4 996 - all seem OK because they have head gaskets that allow more coolant flow through the blocks and less torque (hence less pressure squeezing the piston against the thrust side of the cylinder wall at low revs when the water pump is not delivering full flow). Smaller than 3.4 do not have coated pistons and nor do the early 3.4's but later ones do but seem also to be OK.
It is only (so far) the 3.4 Cayman, 3.6 and 3.8 engines that all have coated pistons, common head gaskets (that reduce flow through the block) and have not increased the flow through the block any other way - so have not increased the coolant flow control slots in line with the increases in power and torque and therefore have to run with that higher squeezing load of the piston to cylinder wall.
It seems that those driven modestly eventually wear away the coating but may continue to run OK or eventually "pick up" damage on the piston face and bore while those driven more aggresively seem to have the coating flake off and jam under the oil control rings - eventually dragging a score down the bore before the piece of coating slides out (I will post some pictures soon to demonstrate the differences).
All the ideas to improve coolant and air flow rates are good but if the thermostat is set at a high temperature before opening - then whatever you do it will restrict the coolant flow by not opening enough to benefit - so the engine will still be running at a high temperature and then when a fast drive is needed - the inertia of the cooling system will still take time to react and probably would not be fast enough to prevent damage since the start temperature will still be too high. So a lower temperature thermostat - is to my mind a must and the first priority - is simple to supply - a bit difficult to fit but by no means as difficult as any other suggestions and can be fitted Worldwide.
Better still when we rebuild engines to increase the flow rate to the cylinders (as we do) but the radiator fan control temperature is not as high on the priority list because a low temperature thermostat means that when spirited driving is used - the start temperature of the system will already be a lot lower than it used to be so by the time the coolant temperature rises - the thermostat opens some more and the cooling kicks in the engine has not risen more than it used to run at all the time normally anyway.
It is true that if you were stuck in a queue then the temperature might rise to 100 or so but then the lower temperature thermostat would be fully open and respond quickly to allow full flow as soon as you drive off and the revs rise whereas even the std thermostat may not be fully open and would soon start closing again - as it works at a higher range.
I cannot guess how much longer a low temperature thermostat will make the engines (that have already run and may already be damaged) - last - but it could and should prevent or delay potential damage.
My biggest concern is that the engines we have rebuilt have been praised for running better than they ever have - suggesting that the previous owner may have been running with some scoring that gradually got worse for some time. This view is reinforced by the high proportion of engines we are checking with a boroscope (before accepting them on our Maintenance Plan) that already have some scratches and damage but show no sign of it in oil consumption or running yet.
I fear therefore that these engines will fail at lower mileages and more numbers than the previous 3.4 996's did (hence our huge investment in repairing them that will take several years to recover).
Hence our best advice to fit a low temperature thermostat as soon as possible and avoid dramatic changes in load - instead building up to a fast full throttle driving speed over a longer period of perhaps 20 or 30 seconds.
Baz
As if by further confirmation of my theory about low revs and slow coolant flow - I set my 996 tiptronic air-con unit to record coolant temp today and drove it at 30 mph on the level in D (when it ran in 4th)and in tipronic mode in 2nd and 3rd - all same thottle opening and load so same temperature generated internally (and you could do the same).
Despite the dashboard temp guage not moving from around 82(and remembering I have a low temperature thermostat) in 4th it recorded just over 1000 rpm and ran at 88 deg, in 3rd about 2000 rpm and 85 deg and in 2nd 3000 rpm and about 81 deg - proving that at low revs the pump does not circulate very well compared to at higher pump speeds.
I did this because we get more tiptronics in with cylinder problems (or at lower mileages) than manuals and I have previously noticed that driving gently tiptronics generally run at lower revs than using a manual because if you suddenly accelerate the torque converter imediately raises the revs almost 1000 revs or if even harder it kicks down.
To make sure a manual is ready to go most people run in a gear that has the engine running about 1000 rpm higher already so tiptronics will generally run hotter for longer and this is exacerbated by the extra torque of a 3.6 or 3.8 allowing good acceleration from relativley low revs.
Baz
Despite the dashboard temp guage not moving from around 82(and remembering I have a low temperature thermostat) in 4th it recorded just over 1000 rpm and ran at 88 deg, in 3rd about 2000 rpm and 85 deg and in 2nd 3000 rpm and about 81 deg - proving that at low revs the pump does not circulate very well compared to at higher pump speeds.
I did this because we get more tiptronics in with cylinder problems (or at lower mileages) than manuals and I have previously noticed that driving gently tiptronics generally run at lower revs than using a manual because if you suddenly accelerate the torque converter imediately raises the revs almost 1000 revs or if even harder it kicks down.
To make sure a manual is ready to go most people run in a gear that has the engine running about 1000 rpm higher already so tiptronics will generally run hotter for longer and this is exacerbated by the extra torque of a 3.6 or 3.8 allowing good acceleration from relativley low revs.
Baz
Baz, another angle -have never seen the inside of the 911 water pump. Is there scope to optimise it do you think? eg 'gas' flow it and/or the plenums to make it deliver more volume? I guess as well all conversations preceding this have assumed it delivers efficiently throughout the rev range, ie the delivery does not fall off badly at low revs and stall out at higher revs -what do you think? Interesting bench test required!
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Yes the pulley looks big enough to be sacrificed! removal looks like it might be interesting -and keep it intact that is!
Further thoughts; cant help thinking others would have been down this trail of investigation before, eg race teams. I checked the parts lists for GT3 & Turbo for evidence of a bigger pump. Unfortunately I cant assess the pump but it and its housing look very different, so thats out unless it can be adapted which is a very long shot. Bigger impeller on same shaft.......?
Further thoughts; cant help thinking others would have been down this trail of investigation before, eg race teams. I checked the parts lists for GT3 & Turbo for evidence of a bigger pump. Unfortunately I cant assess the pump but it and its housing look very different, so thats out unless it can be adapted which is a very long shot. Bigger impeller on same shaft.......?
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