Originally Posted By: bluedevils
Thanks again. Yeah, MN winter blows MI winter away in terms of severe low temps. Sounds like you have no worries about extra wear on winter startup with running Rotella T6 5w40, which I thought was a 'thick' 5w40? If you aren't worried, then I'm not worried.
I find it funny that people who don't own a Bimmer recommend a heavy 40wt oil for them.
Rotella T6 is way heavier than necessary for summer let alone winter use. In winter the oil pump will be in by-pass mode most of the time at higher rev's which is never a good thing.
Under no circumstances is an oil heavier than M1 0W-40 required and although GC is lighter at operating temp's M1's 0W-40 is lighter every time you start the engine cold even in the summer due to it's much higher 185 VI.
Truth is even a light 30wt like PP 5W-30 or M1 5W-30 or M1 0W-30 0W-30 with it's HTHS of 3.1cP (yes that's lighter than the 3.5cP that BMW spec's) will never test the minimum oil pressure spec's for the OP's engine, not the way we drive in NA. The only think of any concern about these oils is that they are not long life oils.