Hello everyone, I have been a long time reader of the forum for help when I have issues I cannot solve myself. Well, now I have run into an issue that I cannot find a solution to from searching the internet. Hopefully someone in here can help me find a solution. I apologize in advance for the long post, but I am going to tell the story from the beginning.

I purchased this Jeep used in February 2022 with 53k miles, it currently has 74k miles as of May 2024.

2013 JKUR
2.5” Mopar lift
33” BFG K02
Mopar cold air intake

Everything started in December 2022 when my radiator started leaking. I caught it pretty quickly and never had any overheating issues. That same month I replaced my radiator with a OEM type Duralast radiator from AutoZone. While I was doing that, I also flushed the heater core, replaced the water pump, radiator hoses, thermostat, and radiator cap at the same time (all with AutoZone products) because most of the OEM products were not available at that time. Everything worked fine for three months, then my temp gauge started creeping up. The gauge would get to the 3/4 mark and then the fan would kick in to high speed and the temp would come back down to the half mark. I don’t have the temp readout as I think that was added the following year model, but the gauge has always ran at the half mark when the engine gets to operating temp and never budges from there. So, I figured the best place to start was to replace the t-stat and radiator cap again. This time I was able to get OEM parts, so flushed the system again and replaced both of those parts with OEM parts in March of 2023. Everything seemed to be working properly again. Until June when the temp started reaching the 3/4 mark again. I have gone through two or three t-stats in the past before I got a working one, so once again, I replaced the t-stat and radiator cap with OEM parts and flushed the system again. Every time I flushed the system, I replaced the coolant with the MOPAR recommended 50/50 coolant/distilled water, always burping the system using a fill funnel letting the engine run for 30-45 minutes, and even raised the front end. I also checked the bleeder valve on the t-stat and only got coolant out, no air. Once again, everything seemed to be operating properly, and once again, three months later I started having the same issue again. I flushed the system again and refilled the cooling system under a vacuum. Since the problem has persisted for so long now, I start checking the coolant level every day via the reservoir as not to break the vacuum on the system. I noticed that the coolant was being pushed into the reservoir but not being drawn back in when the system cooled so I figured I was loosing the vacuum somewhere. I opened the rad cap and sealed the top of the reservoir cap, then forced air into the overflow tube of the reservoir, pushing the coolant back into the radiator through the reservoir tube. When the radiator was back to full, the reservoir level was perfectly art the MIN line where I had filled it to each time I flushed the system. I repeat this process every few weeks just to keep the system from running too low. Eventually, I decide to warranty the Duralast radiator and replaced it the beginning of this month (May 2024). The issue remained, so yesterday I replaced the rad cap, t-stat, and water pump again (all with OEM parts). The problem persists. I have noticed that while driving back and forth to work (30-40 mph speeds) it takes 6-8 weeks for the reservoir to fill up. However, if I take it out on the highway after filling the radiator to full, with the reservoir at the MIN level when cool, after 20-30 mins of highway driving, my reservoir is close to flowing out the overflow tube of the reservoir. I have tested for exhaust in the coolant, and looked over everything for leaks. There are no visible leaks, I am not loosing coolant, the coolant did not test positive for exhaust, there are no warning lights, no codes, no coolant in the oil, no misfires but air seems to be displacing the coolant, especially at highway speeds. The jeep idles good, runs good at cold start and at operating temperature, sounds good when starting from cold and hot. The only other thing I can think of that it could be is the head or head gasket, but as mentioned earlier, I have no other typical symptoms of head issues. The temp has never climbed higher than the 3/4 mark on the gauge.

Thank you in advance for any insight you may be able to provide. I work for a Nissan dealership, and we also own a CDJR dealership about an hour and a half from my home. I will probably send it there if I cannot resolve the issue myself. I have a trip to MERUS Adventure Park and Big Bend scheduled for July 4th weekend, and I hope I can get everything working properly before then.

 

***UPDATE***
I took my Jeep to a dealer to have them pull the heads to check for a leak. Once they removed the right head, there was discoloration on the gasket indicating a slight leak. They pulled the left head and everything looked ok. Neither head was warped or cracked. They replaced the head gaskets, and reassembled everything. I picked up the Jeep yesterday, drove it 90 miles, and the problem has been solved. Apparently the head gasket leak was allowing exhaust into the cooling system, but no coolant was leaking into the head.

 

Thanks for the Update and good to see your issues has been resolved.. Enjoy "JEEPIN".

 

I can't thank you enough for seeing this through to the end. I have the same issue... kid's jeep, overheating, blows head gasket. fixed it, 1 week later it overheats. Replaced radiator, 4 months later, does it again - looks like a bad design - could be lot-related on head gaskets - these heads/engines/gaskets (likely the gaskets - $) may even have had mid-production run design changes (you and I will never know)... I wonder if the late production 3.6 motors see this issue...