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I have a 2015 GC Overland Diesel with 94000km on it.

After driving around town today at speeds of about 30-40km/h I arrived at my destination and shut off off the engine. I then heard a rumble from the front of the car sounding like water boiling. Sure enough it was the coolant boiling in the expansion bottle. The temp was normal the entire trip. Normal being between quarter and halfway mark.

I went about my business and on the way home, kept an eye on the temperature. All appeared just fine. On arriving at home, I left the Jeep to idle and watched the temp gauge rise ever so slowly but never passing the halfway mark, this said the coolant started pushing out the overflow and eventually started to boil. The radiator fan was standing completely still. Turning on the AC, the radiator fan immediately powered on, cooled the radiator and the coolant stopped boiling over. As the coolant contracted, I could see that the level was now too low so I topped it up and tested once again. Same thing happened. It takes a very long time i.e. 10 -15 minutes or so, before the coolant starts to push out the overflow but it happens eventually.

Thinking back, I got the smell of antifreeze from time to time but since I generally drive with the AC on, the condition rarely surfaced. This makes me think the problem has been around since buying the Jeep in 2018.

What I have established so far:
With the AC turned off, when at idle for extended times or very slow driving, the coolant expands to the point where it starts pushing out the overflow.
When this happens the radiator fan is not turning at all.
The coolant eventually starts to boil although the temperature gauge is on or just below the halfway mark. Normal, as I know it, is being just above quarter.
Driving on the freeway, this does not happen. Turning on the AC, starts up the radiator fan and the temps are normal even at idle or in traffic.
This model has no fan relays or fuse located in the fuse box. The spaces where they should be located on the gas models are not in use.
The fan is not faulty because it spins when using the AC and at the same time the coolant situation normalizes.
With the AC off, the radiator fan never turns on. I have not seen it on except for when the AC is on.
I cannot find a relay but I have read somewhere that the fan speed is controlled by the ECU.

The Jeep is out of warranty but still serviced by Jeep. I am however concerned to take the car to them with this problem. I dont want them to start stripping fans and coming with long sad stories. My Jeep is pristine and I just don't want it butchered.

Has anybody had this issue? Could it be the temp sensor reading too low? My best guess is that the coolant temp sensor provides signal to the ECU that in turn, switches on the fan. A low reading would allow the coolant to boil over since the ac fan would never start. I have never seen the temperature sensor in the red. This is my best guess at the moment.

Im also thinking radiator cap. Its hard to believe that it could be faulty. It looks fine?

Anybody ever had this same issue or have any thoughts?
 
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