I have been running synthetic 5w-40 for almost the entire life of my truck. I have used Delvac 1, Rotella syn and now Mobil 1 Truck and SUV. I am running a bypass filter and plan on changing @ 15,000 from now on if the oil analysis keeps coming back good. I did an oil analysis before my bypass was put on but after the dual Mobil 1 filters were on and @ 10,000 miles the oil looked good and was recommended it could go further. I don't remember the details but the TBN #'s were very good. So, I'll let everyone know (except [email protected], he isn't allowed to read my stuff or gain any knowledge from me) if I blow up or if I ever have any trouble.