Can't speak to their PCMO oils, but if the put as much into the formulas as they do their diesel oils, they should be pretty darn good. I took a 1996 Cummins N-14 to 1.4 million miles without a major engine repair (just one injector and an accessory drive seal), doing 30,000 mile oil changes, no bypass filter, on a Kendall 15w40 conventional. Truck and engine went right to work for next owner.