every 3,000 miles and one 8,000 mile interval with 10-40 Valvoline synthetic oil It now has 218,000 and i bought it from the original owner at 197,000. I drive it every day 100-300 miles. I suppose the gunk and crap got off the rings with daily driving at speeds to 75 or so. I'm going back with 10-40 Castrol every 3,000 miles though. The oil gets black at 3,000 miles.