Originally Posted By: FranklinJL
Why is that BMW specs 10w60 for all of thier M-cars? I've seen some v8s and v10s torn down that were ran on mobil 0w40, and 20w50, and bearings and other internals were in great shape. Do you think these engines have fuel dilution issues and maybe that's the reason?
AFAIK, all we really know is:
1. The high-RPM M engines (S54, S85, S65) are intended to survive regular max-output usage, even in hot climates.
2. With that usage, those engines can produce obscene oil temperatures (think 300º F).
3. At those temps, most thinner oils would start to cook off in a hurry. That's uncomfortably close to the flash points of most oils.
4. Castrol's 10w-60 has a LONG development history, including in racing.
5. BMW Motorsport and Castrol developed their engines and oil in parallel. Each one accounted for the other in its design.
Obviously, most people granny the [censored] out of their cars (i.e. don't drive them anywhere near max). They'd never reach the temps at which other oils would fail but TWS would succeed. If I had to guess, I'd say that's why so many S65s and S85s seem totally happy on thinner oils. In fact, I've seen it plausibly argued that the tight bearing clearances on S65s and S85s almost necessitate a thinner oil unless you're always running them balls-out.