Quote:
Originally Posted by YouAreMyWorld
I didn't even know they made a -20 oil, lmaooo. That sounds about as thick as my chap-stick.
With that said however, seeing as how you have an N52, -30 is obviously most ideal for you as it's specifically designed to operate at 200F-220F efficiently. Whereas -40 is designed to operate (N54/N55) at 240F-250F efficiently. However (in case there might be a less knowledgeable member reading), depending on your vehicles spec, a higher 5-XX number does not always equate to outright "better" performance, with the exception of -20 (which is simply trash) for obvious reasons. Reason being is because a thicker oil takes longer to get to operating temperatures and when doing spirited driving, just as how it takes longer to warm up, it takes longer to dissipate heat as well. -40 wouldn't necessarily hurt, but just keep the aforementioned in mind.
That's why many M3 owners opt for a -50 or even -40 for track days, as the OE spec -60 can cause oil temps to stay hot for far too long.
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in the summer, when I had my engine cover on my temperatures would be at 240-260f all the time. with the engine cover removed, I see roughly 210-230f depending on the temperatures outside. since I run without my engine cover during the warm weather, perhaps it makes sense to switch back to 5w-30 oil? but then again, many oils shear down a grade (40 > 30) after about 3000 miles or so.
bottom line, the N52, N54/N55 all recommend you use 5w-30/5w-40, and that these weights are safe to use in all weather conditions (owners manual) being that my car is stored in a heated garage, I see no use in adding oil not specified by BMW.
also, the thing you mentioned about the m3 guys - wouldnt a thicker oil weight lower temperatures? I noticed a reduction in oil temps when switching from 30 to 40 weight.