Getting warm 2011 Cummins ISX on International prostar

First, might consider checking gauge accuracy. If you can use Insite to monitor while loaded and make sure your dash gauge follows closely to what the ECM is seeing. 10-15 degrees above coolant temp is quite normal during a loaded situation. 45 degrees difference is quite a ways off and I agree should be looked into. Did you replace the oil thermostat with the new oil cooler elements? That would be my first place to go next.

 

At this point I think I would put some more miles on it to see if it settles down and keep an eye on it. I think you have done all that you can. If the oil temp gets high enough it will throw a fault. The only other thought would be the proper coolant mix. I have heard of overconcentration causing poor heat transfer but I'm sure with a new engine that you should have a good 50/50 mix if not hopefully premix in it. Just a thought.

 

How much far off could the oil temp even be if the collant temps are ok

There was a drill rig at work a year ago that kept overheating due to another issue. It had a cat motor in it, I was the one to replace the radiator and refill the coolant system. I refilled it 50/50. After that, I kept getting calls from the owner with him saying it was overheating. I said hell I don't know what the hell the problem is, the radiator was just repaired dude. Then he tells me he drained the coolant because a guy from the other costruction company told him to run straight antifreeze in that cat. I said oh jesus Christ. Do what you want dude. Now you just made the problem worse. IT was overheating before hand so it wasn't something I did wrong. A fan blade went through the radiator but was overheating before that. Straight antifreeze has no cooling eefect or maybe minimal