I was using Castrol 10/30 and it would get thin on me and burn a qt between changes. I went to Mobil 1 10/30. Now have 3000 on the Mobil one, full and still clean. Will never go back to Castrol. As for valvoline, it does not fair well on tests. I had a site that compared all the major brands. If I can find it again, I will post it. I think I will try synthetic next.. Mobil 1. the only thing holding me back is the 5 buc price tag... Oh, I also went to Mobil 1 filter. 10 microns... happy car!