996 bore scoring
Discussion
Hi All,
some time ago, Barry from Hartech came up with a suggestion that localised boiling of the coolant under certain circumstances could be a cause of bore scoring.
Over on the Noble forum a guy has experiemnted with a waterless coolant that might be something to pursure here?
Hopefully this will work, if it doesn't then perhaps someone else will cross-post it correctly?
http://www.pistonheads.com/gassing/topic.asp?h=0&a...
Thanks
Andy
some time ago, Barry from Hartech came up with a suggestion that localised boiling of the coolant under certain circumstances could be a cause of bore scoring.
Over on the Noble forum a guy has experiemnted with a waterless coolant that might be something to pursure here?
Hopefully this will work, if it doesn't then perhaps someone else will cross-post it correctly?
http://www.pistonheads.com/gassing/topic.asp?h=0&a...
Thanks
Andy
MTR is correct, it is localised overheating on one bank due to poor design and flow limitations of the channels. Hartech do a decent fix for this after your engine has already lunched itself, so the consensus is to run a 996 until, or ,if ,something goes bang, then get it rebuilt and future proofed. Interesting concept the waterless stuff is, I wouldn't be tempted to put it into my 996.
We currently have this type of coolant under test. The problem causing bore scoring involves many aspects among which are the localised coolant temperatures or bubbling, the cylinder bore material and the piston coating.
If any one contributory factor is changed for something better - this can reduce or even eliminate the problem.
There may be a better piston coating that will survive longer (we are currently testing three new types), there is a better cylinder bore coating (Nikasil) that works OK (and we fit) and if it was possible to reduce the upper cylinder wall temperatures on bank 2 - this can also reduce failures (which we do on rebuilds).
However it is difficult to prove if the problem of the coolant flow is just the temperature or bubbling. Anything that raises the cylinder wall temperature reduces the oil viscosity and allows the piston face and cylinder bore to interfere more and anything that reduces it is a good thing.
As correctly reported - we increase the flow rate through the cylinder block - but only on rebuild.
If the problem is caused by bubbling then waterless coolant would be a great solution but if it is caused just by the temperatures the upper cylinder wall reaches - it would make relatively little difference (but still be better than standard coolant as it also avoids boiling until much higher temperatures so protects the engine if the radiators are perforated or for any other reason the coolant pressure drops).
It seems likely that localised bubbling does occur and that this reduces the oil viscosity that then is too low for the piston coating to resist the relatively rough/sharp/hard surface of the Lokasil. So as it seems likely that bubbling is a contributory factor and as the coolant can be replaced easily - it seems a great way to eliminate one potential cause (or perhaps extend life before failure).
Testing this to establish figures would require hundreds of cars over thousands of miles - but we are testing it as it seems a worthwhile change and we look forward to more feedback over time.
Baz
If any one contributory factor is changed for something better - this can reduce or even eliminate the problem.
There may be a better piston coating that will survive longer (we are currently testing three new types), there is a better cylinder bore coating (Nikasil) that works OK (and we fit) and if it was possible to reduce the upper cylinder wall temperatures on bank 2 - this can also reduce failures (which we do on rebuilds).
However it is difficult to prove if the problem of the coolant flow is just the temperature or bubbling. Anything that raises the cylinder wall temperature reduces the oil viscosity and allows the piston face and cylinder bore to interfere more and anything that reduces it is a good thing.
As correctly reported - we increase the flow rate through the cylinder block - but only on rebuild.
If the problem is caused by bubbling then waterless coolant would be a great solution but if it is caused just by the temperatures the upper cylinder wall reaches - it would make relatively little difference (but still be better than standard coolant as it also avoids boiling until much higher temperatures so protects the engine if the radiators are perforated or for any other reason the coolant pressure drops).
It seems likely that localised bubbling does occur and that this reduces the oil viscosity that then is too low for the piston coating to resist the relatively rough/sharp/hard surface of the Lokasil. So as it seems likely that bubbling is a contributory factor and as the coolant can be replaced easily - it seems a great way to eliminate one potential cause (or perhaps extend life before failure).
Testing this to establish figures would require hundreds of cars over thousands of miles - but we are testing it as it seems a worthwhile change and we look forward to more feedback over time.
Baz
The trouble with the M96/7 cars are well documented, specific temp sensors need to be fitted and carefully monitored under test conditions as the gauges in therse cars are damped in true temp and by reaction time so its difficult for the DIY to assertain any benefit,the pricipal is good and the low pressure obviously is of benefit how this will affect coolant flow stat openings etc Im not sure,also various sensors may need recalibration hence changing,Im sure manufacturers are aware of these products if colder coolant worked perhaps we would be running R32 or somesuch refrigerant,also metals react more when peramaters differ such as cold coolant in a hot engine so its a difficult issue with detalied analasis needed long term.
Hopefully Gary you will be aware that we extensively tested two engines (with and without several modifications) and fitted with temp sensors - several years ago before understanding the issues with the false temperature readings and differences in the coolant temperatures in different parts of the engines and while testing what modifications will help reduce the problem.
Low coolant pressure is a bad thing with standard coolant as it lowers the bubbling and boiling point (which is not the same thing). A cracked expansion tank, leaking cap, damaged coolant pump or drive or a leaking radiator (or pipe connections) can all lower coolant pressures before the owner realises it and could result in scoring before the owner has a chance to put things right. Waterless coolant would prevent this happening. It can also prevent bubbling or boiling even under atmospheric conditions until a much higher temperature is reached than these engines are ever likely to reach.
The problem with bubbling is that it insulates the surface from the coolant and allows rapid localised temperature rises - of the type that might well explain the reason why bank 1 lasts so much longer than bank 2.
My view is anything that has a good chance of contributing to longer term reliability - that is not too expensive - must be a good idea.
Baz
Low coolant pressure is a bad thing with standard coolant as it lowers the bubbling and boiling point (which is not the same thing). A cracked expansion tank, leaking cap, damaged coolant pump or drive or a leaking radiator (or pipe connections) can all lower coolant pressures before the owner realises it and could result in scoring before the owner has a chance to put things right. Waterless coolant would prevent this happening. It can also prevent bubbling or boiling even under atmospheric conditions until a much higher temperature is reached than these engines are ever likely to reach.
The problem with bubbling is that it insulates the surface from the coolant and allows rapid localised temperature rises - of the type that might well explain the reason why bank 1 lasts so much longer than bank 2.
My view is anything that has a good chance of contributing to longer term reliability - that is not too expensive - must be a good idea.
Baz
hartech said:
Hopefully Gary you will be aware that we extensively tested two engines (with and without several modifications) and fitted with temp sensors - several years ago before understanding the issues with the false temperature readings and differences in the coolant temperatures in different parts of the engines and while testing what modifications will help reduce the problem.
Low coolant pressure is a bad thing with standard coolant as it lowers the bubbling and boiling point (which is not the same thing). A cracked expansion tank, leaking cap, damaged coolant pump or drive or a leaking radiator (or pipe connections) can all lower coolant pressures before the owner realises it and could result in scoring before the owner has a chance to put things right. Waterless coolant would prevent this happening. It can also prevent bubbling or boiling even under atmospheric conditions until a much higher temperature is reached than these engines are ever likely to reach.
The problem with bubbling is that it insulates the surface from the coolant and allows rapid localised temperature rises - of the type that might well explain the reason why bank 1 lasts so much longer than bank 2.
My view is anything that has a good chance of contributing to longer term reliability - that is not too expensive - must be a good idea.
Baz
Hi Baz my reference to the low pressure was only using the water replacement (hence higher boil point) I agree low pressure due to a fault in a standard scenario using water as coolant is bad particularly in these engines where flow and heat dissipation is questionable to cylinder 5-6....now youve made the point though I think your right the only benefit maybe being perhaps able to remove expansion tank when hot,I have to say though when very hot these engines do stretch the rads,caps and hoses would that not ease with this coolant replacement perhaps not?Low coolant pressure is a bad thing with standard coolant as it lowers the bubbling and boiling point (which is not the same thing). A cracked expansion tank, leaking cap, damaged coolant pump or drive or a leaking radiator (or pipe connections) can all lower coolant pressures before the owner realises it and could result in scoring before the owner has a chance to put things right. Waterless coolant would prevent this happening. It can also prevent bubbling or boiling even under atmospheric conditions until a much higher temperature is reached than these engines are ever likely to reach.
The problem with bubbling is that it insulates the surface from the coolant and allows rapid localised temperature rises - of the type that might well explain the reason why bank 1 lasts so much longer than bank 2.
My view is anything that has a good chance of contributing to longer term reliability - that is not too expensive - must be a good idea.
Baz
Gassing Station | Porsche General | Top of Page | What's New | My Stuff