It really doesn't matter. Buy Walmart branded 15w40 diesel oil, keep a check and don't let it get too low, change a time or two each year. Enjoy life.
My Cummins diesel powered '95 dually has 300,000 miles. I used to obsess a bit on everything about my new baby, only ran Valvoline Premium Blue (from the local Cummins dealer) did oil analysis, installed a by-pass oil filter, turned the fuel up a lot (more than doubled hp) drove the crap out of it. For the last 100k miles I've followed the advice in the first sentence above. No oil issues ever. And this is on an engine that's been worked like a dog at times. Max power, 3rd gear for miles at a time pulling a trailer in the Rockies. Our AD trucks live a life of pampered leisure in comparison.
Just make sure it has oil in it and don't use 5 or 0W anything.
RonR
