My dealer mechanic told me that full synthetic would be a better choice if you can do it because the oil doesn't break down like dino does under extreme temperatures, BUT he also said that it wouldn't hurt your car if you don't use it, and you must still change your oil at the same interval as dino. I have used it several times and can't tell a difference, BUT one can't immediately tell a difference when you can't see inside the engine to see the effect.

Bottom line: I do try to use at least half sythetic. What I have used is Valvoline 5w-40 full synthetic or 5w-30 half synthetic.

JMO

Rick, Denver, 97 850-R, 70,000 miles original owner, zero problems