I run Rotella 15W40 in both my 3126B, Rotella 10W30 in my D7 and Rotella T-6 in my Detroit powered Argosy and Rotella T-6 in my Gehl skid steer (I'm a little stuck on Rotella) I Chevron Delo is also a very good product, Cat leans towards their own DEO 15W40 and 10W30 for land engines.