Mobil 1 with the RED cap used to be ok but check for the "energy conserving" circle just to be sure. IF it's on the bottle do NOT use it. I use Shell Rotella T in the BLUE gallon jug. It's a full synthetic and Walmart usually carries it for about $12 a gallon. When I find it, I buy 2 or 3 just to be sure I have some. I've also used Royal Purple, but I think it's pricey too.