the volkswagen and saab specs I found indicated nothing more than 10/40, actually 0/30 or 5/30 was the recommended oil for both of them. 20/50, wasn't even on the radar. even heavy diesels don't specify oil that heavy, although the largest diesel engine I have ever worked on was only 7500 HP but they ran 40 weight in those. So I'm not really sure how to compare those apples and oranges....
