And just when you thought you were happy..... I find the information I was looking for!
Not quite as I recall, but it would appear (and remember this is in relation to Corvettes) that a different weight oil is called for in Europe compared to the US. The standard would appear to be different?
Let me know what you think after reading it, but my opinion is that you should use US spec oil of the correct weight, or EU oil of a different weight (0W 40 vs 5w 30) because there would appear to a difference........
I spent about an hour looking at various sources, and still cannot fully, and with complete confidence, answer whether or if so, why, GM might recommend Mobil1 0W-40 in Europe. I have sent an email to a GM contact, but he is not directly linked to Chevy or Corvette, so may not be able to answer either. If he does, I’ll post again later. Here is what I did find. Yes, the Mobil1 Europe site does say 0W-40, and with their association with GM, that implies GM is ok with it. But implications are not certainties, and I could not find anything that I’m certain was stated by GM that said 0W-40 (I’m not certain whether the sticker that was pictured earlier in the thread was from GM, Mobil, or some other source). Mobil1 0W-40 does meet ACEA A3 spec, while their 5W-30 does not. The A3 spec specifically refers to high performance engines, so it makes sense that in Europe, where that spec is publicized and considered important, Mobil would want an oil being proposed for a high performance car like the Vette to meet A3. I could not find any comments by GM about A3 spec. The portion of the A3 spec that Mobil1 5W-30 fails, has to do with viscosity at ultra high temperature. Since I could not find definitive statements from Mobil or GM, I must now get increasingly speculative.
For some reason, perhaps driven by manufacturers like Mercedes, BMW, Ferrari, etc, and perhaps driven by more high speed Autobahn driving, the European spec setting agency ACEA may look further than US standards into the ultra high engine temperature regions. Indeed, GM sources in the US say that 15W-40 is OK for Vettes under track conditions with ultra high engine temps. But the trouble with 15W-40 in street use is that it’s thicker than you really want when starting from cold. And the trouble with 0W-40 in any use is that to get to that wide a viscosity spread, it must use a lot of VI improver, which has disadvantages as noted in my earlier post. So here’s what my best guess is right now. Mobil and GM both clearly agree that in the US, the best compromise for all but track use is 5W-30, and go to 15W-40 if you are going to the track. And note that hot days like Phoenix are not as severe as the track, so even Phoenix on the street would be 5W-30. Neither GM nor Mobil likes 0W-40 for street use in the US due to the VI improver issue. In Europe, due to the greater publicity of the A3 spec, Mobil considers it important to meet that spec, so they are willing to accept the disadvantage of added VI improver in order to have their oil meet the A3 ultra high temp spec. It is not clear to me whether GM agrees. But what does seem clear is the following. If you use 0W-40, the two small advantages you gain are a bit more protection at ultra high engine temps (ie, racing, not hot weather), while simultaneously having a bit more cold start protection for sub zero cold starts. But the price you pay is an oil with more VI improver to get the 40 spread of 0W-40 instead of the 25 spread of 5W-30. For my part, I would never put a 40 spread oil in my car because of the VI improver problem. 5W-30 is perfectly ok for hot weather, and even for a few laps at the track, and if for some reason I wanted to race the car where oil would be ultra hot for hours, I’d change oil to 15W-40, and change back when I got back on the street.