Quote:
Originally Posted by JEllis
Is there some evidence somewhere that lighter oil is preventing early bearing failure? What about those of us that consistently run their cars at very high engine temps? Maybe the M5 guys have some data?
I understand the logic of a thinner oil getting into tighter areas. That being said our engines run at 210 degrees which is HOT to begin with. On the track our cars are typically operating around 255-270 degrees. What are the lubrication benefits of a 40 weight oil vs. a 60 weight oil at 255 degrees? I am aware that both oils fall within a wide envelope of operating temps but how do the viscosities of both oils compare when at the higher temps?
This rod bearing issue sounds a lot like the Intermediate Shaft (IMS) issue that Porsches with the now antiquated M96 engine (986, 996 and 997.1) had. Many IMS issues were believed to be a result of IMS bearing failure that caused the IMS to wobble and eventually cause catastrophic failure. Except with that issue one of the solutions is (theory) to switch to a heavier weight oil. The belief is that a heavier weight oil will maintain viscosity at higher operating temps and stave off excessive bearing wear. One of the leading beliefs was that the recommended Mobil1 oil did not maintain its advertised viscosity and thus the recommendation was usually a higher quality oil or a switch to a heavier weight oil.
I understand that part of the argument is the cold start issue. I completely agree that during a cold start, especially in a cold climate, the effectiveness of the 60 weight oil is questionable. That being said, I feel this is why it is extremely important to allow the S65 to warm-up prior to any kind of real load is placed on it. Furthermore, if we swap to a lighter weight oil for the 10-15 min the engine is warming-up... what is the lighter weight oil doing at standard operating temps which accounts for 99.9% (rough guess) of actual engine use.
So is it better to have a lighter weight oil to protect the engine during a cold start at the sacrifice of viscosity/lubrication at operating temps or beyond... which accounts for the vast majority of engine use?
If we can agree that the most vulnerable time is during a cold start is it possible that some of bearing failures may be a result of not following a good warm-up strategy? I am not talking about bouncing off of the redline below 210 degrees, I am talking about avoiding any kind of high revs at all until the engine hits 210 degrees.
I would love to see data other than logical speculation? Because otherwise I can logically explain why we should stick with a heavier weight oil, that there is going to be a certain percentage of mechanical failures regardless of what we do, that some owners do not wait for their cars to warm-up, I would be shocked if bearings removed after 60K miles did not show at least some wear and that in the end the failure rate of the S65 is quite small despite how much this forum amplifies the issue. Granted I am willing to admit I could be totally screwed up.
Jason
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A lot of it was discussed here and I provided bearing specs and measurements, BMRLVR provided engine building expertise, and kawasaki provided both engine building expertise and oil analysis expertise.
http://www.m3post.com/forums/showthread.php?t=856441