i use 10w-40 high milage oil and works great, the diffrence i have seen sence starting to use it for the past 2 years is i have seen better milage, not much but a little better, and most noticeable is the burning of the oil, it does not burn as much thats it, and i got a oil gasket cracked before on the oil pan when i hit a rock and it starting leacking through and thats when i chanced to 10w-40 high milage and what i saw also it stop leaking, so i guess it's thicker as well. but i have been thinking if i should change to full synthetic soon, to see if i see a diffrence.