I have been using Valvoline in my Dmax. I did my first oil change at 3k. I put in Valvoline Premium Blue 15w-40. It is not synthetic, however it does state that it meets or exeeds every leading diesel manufactueres standards. CH-4, CG-4, CF-4, CF/SJ,. It is also recommended and endosed by Cummins. I have not had any oil related problems yet. I am at 21k.