I always used Mobil 1 in my 2002, 2004 and 2007 Duramax. Mobil 1 has changed their diesel oil to 5w40 rating, there is no longer a 15w40 Mobil 1. I also used the oil life monitor to recommend change intervals. The 2011 Duramax requires 5w40 synthetic, this wil... Login to read more.