- Feb 23, 2006
- Fairbanks, AK
I have a 98 Z-28 and religously change out the Mobil 1 every 3K. (It's for peace of mind, I know it isn't necessary. I get about 1 MPG after a fresh oil change. I get about the same results (1 MPG increase) with my wife's Mountaineer, but it gets 5 oil changes.