Quote:
Originally Posted by GuidoK
But the s65 also has that same bearing clearance that the n55 has, and for that BMW recommends 10w60, just as for the s54.
Maybe ideal oil weight is more than just bearing clearance?
Have you done a lot of miles/km in your z4m with the thinner oil? (like 50k km or more?)
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Oil weight depends on more than bearing clearance, yes. S54s are notorious for running hot because of inadequate cooling, both oil and water. The cooling on my E46 M3 race car is very good, that's why I can run an oil that's more suitable to the bearing clearances used. On a standard car I wouldn't run 10W-40 because of the poor cooling. If I didn't have 30L Castrol 10W-60 laying around I would run 5W-50 on my Z4 M because it's not driven very hard. A track car without proper cooling 10W-60 is nothing more than a band aid, but a must if you want the engine to survive. Same goes for the S65, inadequate cooling combined with a high RPM engine means very high temps.