I've been doing my oil change on my previous cars using 5w-30 or 10w-30 not even thinking if it's the right one.. And just lately since I will be changing oil on my 335, I tried to look around for a good one and found 0W-40.. Saw that it's recommended for turbocharged or supercharged vehicles.. BMW LONGLIFE OIL 01 approved as well.
Here's the specs:
Check out the Q/A thread at Mobil1:
The following is also a thread but pretty much not a BMW vehicle. Check it out too cause it kinda talks about temperatures "Cooking" on turbo engines:
Anyway, just my two cents..