Europe does not allow group 3 oil to be labeled synthetic. U.S. does. What that means is most Castrol and Mobil 1 sold here in the U.S. labeled as synthetic really aren’t completely synthetic…
Almost all of the synthetic oil don’t meet European auto manufactuerer requirements (VW 502/505 or BMW LL01 for example)….[/quote]
I’ve torn down 2 Subaru engines. 1 used synthetic oil all it’s life, and the other conventional. The one that used synthetic was pristine clean inside, while the one that used conventional was full of sludge. I was sold on the benefits of synthetic at that point.
