So long as the ambient temp is above 10F I would go with the 15W50! It is going to be less volitile and should protect better under sever conditions. The 15W50 should also have a better additive package. Last I just will not run a 20Wt reguardless of if it has a 0 or 5 W proceeding it!
This question a loaded questionthough because idealy we could use more information. If warranty is an issue then the 15W50 may cause you grief if their ever was an issue with the engine.
If I had a modular Ford design type engine, M1 0-20. Everything else, M1 15w-50. But remember, I live in the deep south and have a depleated uranium right foot.
[ May 29, 2004, 08:46 PM: Message edited by: 427Z06 ]