I recently opened an account with
AMSOIL just for my personal use. At their local wharehouse, the manager there told me that Mobil1 was basically a 10,000 mile
oil.
Amsoil's original
synthetic is a 25,000 mile
oil, and their new
Amsoil 2000 series is a 35,000 mile
oil. They said the 0W-30 offers more protection than a 20-50W. Oils don't break down, it's the contaminants in the oil. Amsoil has a cool by pass filter set up that filters down to 1 micron or less. I'll change my oil once a year whether I need to or not.
Ed