Jr, I used Mobil 1 5-20 full synthetic 'till someone on here posted a link (wish I had saved it) from Amsoil or Royal Purple, I can't remember which. It broke down all the top full synthetic oils and blends from top to bottom. Of course, Amsoil or Royal Purple was at the top, with Castrol syntec the first or best (Walmart) brand listed. It beat the next one, which I don't recall now, by quite a bit. I'm sure any 5-20 syn. oil would be good, but the numbers form that comparison were lop sided enough to sell me on Castrol. just my 2 cents.