My 2000 Buick Regal, Series II 3800 V6, states 10W30 right on the oil fill cap. I had a good uoa with Mobil 1 10W-30 and should have one coming up soon with GC 0W-30.
My owners manual specifically states to not use other grades and specifically says not 20W-50.
I like this engine. I don't know if a 20W-50 will cause problems, probably not, but you will have sluggish performance and waste fuel. I tried Castrol 10W-40 Synthetic and it is a very light 40wt. It works.
Don't know why experience would be any different in OZ.
I'd just say no to 20W-50.
These engines are very easy on oil and I think something like GC is a perfect match. Anything thicker is just not needed.
I don't think it's all about CAFE here on this one at all. I think GM isn't convinced on 10W-40 dino quality here due to past performance and 20W-50 is not needed. The manual suggests you may consider using a synthetic 5W-30 in extremely cold conditions. That wouldn't apply down under.
[ May 04, 2005, 12:06 PM: Message edited by: haley10 ]