lunchbox660 said:i use lucas and mobil 1 15W50 in my engine and my puppy runs fabulous, i get about 35 miles per gallon now when i dont stomp the throttle all the time...of course, who wants to drive like that all the time? LOL, but no, seriously, i do alot of traveling, and the hi MPG is VERY apparent on the highway. i can get about 350 miles out of my tank before the gas light comes on. wether or not it hurts or helps an engine, i dunno. its a very thick fluid, so i DOUBT it hurts it. if anything, it prolly helps it since it is a thicker fluid, chances are it holds a better seal and will not break down as easily as plain oil.