I had a problem I cooke city mt one day -35 with 15-40 WOW had to start the truck several times to have it keep oil pressure. I run 5-40 In all my diesels now

 

I have been running Schaeffer's 5w-40 and 15w-40 in the trucks for about 8 years. One is full and the other is semi-synthetic, Full in the Ramchargers and semi in the 2500. I also use Fleetguard Filters. If it matters in the two Indian's also! I've had no trouble at all doing an annual oil change. Buy 1 Oils has free shipping over $75.00 right to the front door.