I know I don't have a dog in this fight but FYI...Cat and Detroit both come factory filled W/ Mobil Delvac.....NON-synthetic.
They might not come from the factory filled with synthetic but I have plenty of class 8 customers using it. With fuel at $2.50 a gallon if a truck can gain just .5 mpg thats a big saving, and yes that is the norm and I have a few that switched everything over and gain .9 mpg. Either way that gain pasys for the oil plus better protection.


Greg