Originally Posted By: Brigadier
Protection vs CAFE....
I'm not sure it's quite that simple.
The EPA requires the manufacturers to do everything in their power to ensure that the lubricant used by owners is the same lubricant used during the initial fuel economy certification. They do this buy specifying that particular grade in the owner's manual. I think this is one reason why you don't commonly see oil viscosity grade ranges anymore (like 5W-30 for under 50*F, 10W-30 for above 50*F, etc). I also think this is why you see lighter grades being specified in the United States than in other parts of the world. It's not necessarily that they don't protect as well (especially for the slower speeds being driven in the US), but that the lighter grade is the lubricant used during fuel economy certification, so they're compelled by law to recommend the use of that lubricant in the owner's manual.