Originally Posted by cary

Note that that 35k is subject to qualifications:

1) That you peform regular oil analysis to make sure the oil isn't breaking down,
2) Vehicle is not operated under severe circumstances (or else drop to 15k), and
3) the oil is not used more than 1 year.

Amsoil makes a good oil, but it is no better than Mobil 1. In fact there was a test run (called the space bears study on bobistheoilguy) where the guy ran the oils for about 18k miles with analysis every 1k miles. Guess what, as many have found, Amsoil thickend out of grade over time while the Mobil 1 continued to stay in grade, offer lower wear numbers, and maintain its TBN. This while being cheaper. It is hard to beat Mobil 1's R&D.