2015 ISX15 high oil temperature

[tree98]

Oh boy, I don't know where to begin here.....
First off, how was it determined you were getting oil in the coolant?

If you're using 2 gallons of coolant and 1 gallon of oil EVERY DAY you are in serious trouble man!!

Your dpf is likely ruined at this point from the coolant washing away the precious metals in it. Also must be a LOT of oil residue on the dpf(or maybe it'sall over the engine from blowby?), I can't believe this thing has been able to regen for quite a while.
Has it been asking for a parked regen?

250 degree oil temp and kenworth says that's normal?? Yea ok I guess I'm not surprised they would say that but it's definitely not normal, it's a sign of high friction somewhere.

This engine obviously has been neglected and now you have all these problems that might or might not be related.

I would start by pressurizing the cooling system to 20 psi let it sit overnight and fix all the external leaks, while your at it drop the pan and look for coolant running down the cylinder walls on one or more cylinder's from bad injector cups.

How many miles on this engine? While the pans off you need to roll in new bearings if your at 800K or more.

Pull the dpf and doc, post pictures of the faces here so we can see if theres evidence of oil or coolant, then you can take them to get baked and flow tested, while they are off start the truck and see if it's burning oil and smoking badly.

I'm sure your due for an overhead adjustment as well as an EGR tuneup, Rawze has videos on both at the top of the screen.

You have some work to do if you want to straighten this thing out, and don't rely on the kenworth stealer to get it right because all they'll do is drain your wallet. Your other option is drive it/tow it down to Mr Haggs shop in GA. if you want it done correctly by pros.