Going to 5w40 amsoil year round here. When looking at this remember how oil viscosity is measured. the 5w and 15w are cold weights. The 40 is the lubrication at operating temp. So when its warm the 5w40 and 15w40 are the same. the 15w is just thicker in cold temps
so far I've been very happy with my 5-40 Rotella. I have about 4k on it and the truck is still running good. Before I had 5k on Castrol and my MPG's fell like a rock after 4k, and it was getting loud. Switched to the rotell and haven't looked back since. hoping to get 5-6k out of my rotella.
im running rotella 15w40 now, but in my search for AMSOIL synthetic, i was recommended the HDD 5w30 year round being up in NH because of the varying temps throughout the year here.
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