So I have a 15 jk, I have been having some trouble with my the engine running hot. My coolant temp will get all the way up to 240s (3/4 on temp gauge) before fan kicks on and it takes it down to low 200s. After it takes it down it will baseline around 222 and uphill slops will take it up to 230. I’m running a 6in lift with 37/13.50s on Dana 30 in front and 44 in rear (just hit 100k miles) This temp is interstate driving 65-80ish mph, I'm in 5th gear most of the time but shifting to 6th doesn’t help with the temp any. Thermostat went bad and was replaced 15-20k miles ago and I just replaced a leaking oil cooler. Still having this issue. Any help would be greatly appreciated!

 

Welcome to JKF. Was temp ok before failure / replacement? What temp thermostat? MOPAR or Aftermarket? Have read several posts on replacement thermostats failing..Do you have any CEL or codes? Does the fan kick on when Defrost or AC is ON - it should. Temp sensor..

 

You mentioned " I'm in 5th gear" tells me you may not have the right gear ratio to be able to turn those 37" tires efficiently. Running in 5th gear will keep engine RPM's higher than they need to be, thus building heat in the engine. Even with the proper gear ratio the 3.6L will run on the higher (hotter) side. While I do not know when was the last time the coolant was changed out, I would also consider dumping the old coolant for some fresh Mopar coolant. We assume you have eliminated head gasket leakage ?

 

In general, I would say what you're seeing is not abnormal if it was dead of summer and temps were ~100°. Not sure which "Bristol" area we're talking, be it England, PA, VA....I'm pretty sure it's not 100° there right now. Since you just did the oil cooler, and since coolant runs through that cooler, I would double, and triple, check that I had zero air in the cooling system. These JKs are hard to burp and I'll typically pull the radiator cap for 3-5 mornings just to check if coolant is all the way up there.

You didn't really mention if this is something that just started and you think could be related to recent work or not.

 

Just thought about this post the other day and figured I’d give an update. Swap gear in the rear to 5.13s, axle swapped the front axle to a Currie 44 with 5.13s. Upgraded the front and rear drive shafts to Tom Woods 1310s. Jeep runs and drives great now lol. No temp problem after axle/gear swaps.