(2014) ISX15 coolant help!

[redbeard]

Sounds like it was doing a passive regen in your last two statements. Was the high exhaust temp light on? How about the turbo, was it chuffing at idle and the engine sound pissed off and not smooth and happy?
When mine does the passive regen, throttle response is sluggish at idle and sounds like timing is adjusted and the engine is fighting itself up till about 800rpm, then smooths out. High temp exhaust light is almost always on when this happens, and turns off when over the 800ish rpm and accelerating thru gears.