k, so here's the thing.
I bought a 2002 Dodge 2 wheel drive with 480,000 km (290,000 mi) on it
It is in overall very good condition and I really really like it.
I bought it about 4 years ago with the intention of just being my tow vehicle for my 4 ton 5th wheel.
I recently started using it as my daily driver and will be for a while

The climate I live in can get to -40C (-40F) in the winter and +35C (100F) in the summer

I don't have the maintenance records from the previous owner(s) and I don't know what oils have been used on the truck.

For a little while, I was using Shell T6 but developed a ton of oil leaks and I think there is LOTS of blow-by now.

I'm kinda nervous about the blow-by and don't want to spend a ton of dough and rebuild the engine.

I am now using Shell 15w40.
I've researched it to death on the internet and have asked some die-hard cummins dudes about what is the best oil to use.

I have a stock 2002 Cummins 5.9
What is the best engine oil to use to hopefully ensure that I get another 500,000 km from that engine.

Thanks

 

I have a 2001 Ram 2500 5.9 Cummings Diesel, it has 118,560 miles on it and what the diesel mechanics have told me was to use Rotella as my engine oil all the time and have never stopped using it. I do know if you start changing to different oils you will start getting leaks or other problems. I also change the oil EVERY 3000 miles. It does get down to 25 -30 below zero here at times. When the outside temp is to reach 35 deg F or lower, I always plug in my engine heater. Never have had a problem starting it no matter how cold it gets and no oil leaks at all.

 

Shell Rotella T-6 is good stuff. Ive been using it for years. Ive used other syn. oils such as Mobil-1, and Chevron Delo 400 when Rotella T-6 wasnt available. And, I only use Fleetguard and WIX oil filters exclusively. I have over 156k miles on my rig, and not one single oil leak.