ok, so a mate and me were "discussing" about weights of the oil. i currently use a 10W60 in my car. I used to use a 5W60 in my car. He said its too heavy and i'm damaging the engine. I say that the only thing thats hurting is fuel economy but i get better lubrication and protection. I choose that over an engine rebuild. i used to use a 5W40 and i suspect that this is the reason why fuel economy went down. anyways am i doing damage? did some googling research and websites saying the same thing: thicker oil is better at lubricating but at the expense of mileage. discuss.