The gauges in my VW porsche powered bus, and my porsche 914-6 tell the truth. Both engines are air cooled, and have oil coolers. Both engines run cooler with mobil 1 15-50. Also both engines hold 10psi more oil pressure over the regular dino oils the M1 replaced when hot. Oil temp in the VW bus pulling mountains would go to 250F sometimes. Never goes over 210F now. End of story for me. Everything gets it after break in. Cheap insurance, and the oil handles the higher tempertures. If you want to see some real results, pull the intake manifolds of like mileage VW TDIs. One with sythetic, other with dino. Observe the thickness of the coke layer on the intake runners.