I have been told it is a good idea to run 15w40 diesel oil in a high mileage 4.0. I run the 15w40 Motorcraft oil in my 7.3 Powerstroke and it would be nice if I could use the same oil for both vehicles.

 

15w seems high for an engine that sees a lot of wear at start up.
Salad created this:
https://www.cherokeeforum.com/f2/rot...essing-188168/

 

Run Rotella T6 5w40 or T5 10w30.

 

i use store brand 5w30 yr round, have for the entire time owning them

 

i use 15w40 in mine in the summer, Delo 400 since its free and my engine has 190k on it have never had any issues , and i normally run 10w30 Rotella in the winter

 

I normally use 15w-40 year round, but Amazon had a sale on a new Delo 15w-30. I'll give that a try this "winter" in GA.

 

I tried 15-40 but it was too thick for me. So I switched to 5-40 Rotella T6 and run that year around with great results. I have almost 284,000 miles.

 

I personally use Rosella T 15-40 but I live in South Texas and the past 3 months have seen temperatures above 95 degrees. Heck even with a COLD ENGINE my Thermostat reads like 150 before I even turn on the JEEP LOL.

 

10w40 works really well in my jeep.

Closest I can find to that is 5w40 Rotella T6 which is what I run pretty much year round. If I am cheap and need a quick oil change I will go with 15w40 in the summer but I have to swap it out before it gets cold in Colorado (usually mid september we start seeing low 40's in the early morning).

 

Won't hurt a thing.....I run it in mine. Most all agri equipment runs fine with it. The 4.0 is as close to a tractor engine as you will ever find!
As long as your starter will spin the engine when cold your good. The theory about not getting lubed when cold does not mean much. The residual oil left on bearing surfaces will be adequate lube for several minutes! Just allow a little time for engine to warm up a bit.

 

he said tractor!

 

With seven main bearings plus stiffening plate,deep sump, excellent lube distribution and reports of 500k miles it may be BETTER than some tractor engines.