Used to be delvac and rotella were head a shoulders above the rest, but read up on ck-4 oils, the API made all shelf oils uniform. What used to set Amsoil apart was the interval, super high tbn that allows for longer interval, not really sure any of that is happening with diesel ck-4, have not looked into it. So bottom line, if it were me I would only run synthetic oil, no blends, if it doesn't say synthetic oil like t6 does, then it isn't synthetic. So much confusing with diesel oils, look for synthetic. Just a quick look, it is hard to think you can do better then t6 which is 71 bucks 3 gallons, I doubt you will find better or cheaper. I looked up Amsoil which is showing 1200ppm CA, which means API effected this formula. Amsoil SS is 43 a gallon with discount, so in the grand scheme of things it is six and a half one dozen of the other. I might go Amsoil if I was pushing the interval, but if you are under a 10k interval, I'd probably just keep doing what you are doing. With diesel you get more return on filtration then oil choice. Bypass, run a double, or bypass all in one, lots to consider there. If you do chose Amsoil, make damn sure it is a synthetic one, most of their oils are not.
