From what i've seen is it works good for lower mileage engines, not for worn high mileage engines. I've known people to use it and next thing they had oil puking out of everywhere. All oil companies say that you can run it with no problems, but will stick to regular oil, cause I can't see spending the price for it. A mechanic buddy of mine tried it once and it knocked a bunch of sludge loose and plugged up his oil pickup and killed his high performance motor!
He was not happy! One good report I've seen of synthetic is it does increase mpg!
