Wasn't that Delo, or am I confusing it with another brand?Although I use Rotella 5w40 T6, year round in my 2011 3500, if I were using 15w40, I wouldn't have any issues using the Kirkland 15w40. It's also interesting that Kirkland now is using Chevron for it's supplier. I've used Chevron 15w40 when I owned my 2002 F350 7.3 Power Stroke, good oil.