2015 ISX15 high oil temperature

[JimT]

What kind of miles are on that truck? In addition to what tree98 said above:

2016, I'm assuming that's a cm2350, so has the fuel pump ever been opened up to inspect the head, plungers, tappets and cam? They are a known source of engine damage and complete failure after about 400,000 miles.

It's possible you have an issue with your oil cooler. Could be clogged up with debris (especially if your fuel pump internals are chewed up).

Excessive soot build up in the oil and/or extended oil drain intervals could have accelerated wear on the bearings and cam leading to increased friction and more possible debris collecting in the oil cooler.

Excessive blow-by could also be adding more heat from combustion directly to the oil.

Also, has this truck had any custom tuning? Was the HP and/or torque increased? That could lead to higher oil temps too.