To the OP, do you have your oil analyzed? That's the only real way to tell how it's performing. My last analysis of Amsoil Metric 10W-40 fully synthetic at 9,300 miles showed the cSt 100C at 13.8, hands down better than Mobil 1 4T Racing at 6,100 miles. The Amsoil has proven best at the least viscosity shear-down of the three oils I've used including the Mobil 1 and BRP XPS synthetic blend.