JKU Rubicon Overheating - JeepForum.com
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post #1 of 8 Old 08-26-2017, 12:01 PM Thread Starter
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JKU Rubicon Overheating

Hey there everyone! I've been a lurker for sometime on the forum, just trying to soak up as much knowledge as I can, but now I need some assistance myself.

I have a new to me 2011 JKU Rubicon, and it has an issue that baffles me. When sitting still in the sun for about 5-10 minutes, like at a drive thru, it will start to overheat and the AC compressor clutch disengages. Now it doesn't over heat to the point where it starts smoking and barfing coolant all over the place, but the temp gauge does go past the halfway mark. For instance, during normal driving the gauge gets to the 12 o’clock position and stays there. When I’m sitting for a while though it gets to about 1-2 o’clock and that’s when the AC compressor clutch disengages. Once I start moving again it cools right back down to 12 o’clock, and the clutch re-engages. Now to answer the question, “Which came first, the chicken or the egg” it seems the engine starts overheating, then the AC clutch disengages. Now it occurred to me that this may be a “safety feature” that when the system detects an overheating engine it kills the AC to keep the engine from maxing out, and if that’s the case, then I need to start looking at the cooling side of things and start diagnosing the overheating situation. What do ya’ll think, have any of you heard about this? Could the AC clutch be that sensitive/ worn that when it starts to get too hot it slips and no longer engages? Could my compressor be on the way out, and this is simply an indication of that?

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post #2 of 8 Old 08-26-2017, 12:06 PM
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much has to do with if the system has been taken car of. People tend to never change the rad fluid, kinda like an auto trans. they only time they do is when something goes out.

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post #3 of 8 Old 08-26-2017, 12:53 PM
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Have you checked the coolant levels?
If you need to add, make sure you get the correct coolant.
Check the manual but I believe yours will use an HOAT formula.
Somewhere around 12 or 13 they switched to an OAT formula.
They aren't compatible to mix. Neither is Si-OAT.

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post #4 of 8 Old 08-27-2017, 06:27 AM
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Sounds to me like you have a flow problem. You're simply not circulating the coolant properly. It may have never been serviced by the previous owner, so you may have buildup in your cooling system. Coolant can only last so long before it starts to break down. That can impact everything from your radiator to your water pump.

Anout your AC compressor, I'm not sure about that one. It may be a safety issue that automatically shuts it down once your temp reaches a certain point. But, I think that's a secondary problem to your temperature, and may actually take care of itself once you correct your cooling system.

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post #5 of 8 Old 08-27-2017, 10:05 AM
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With it all warmed up, ignition off, turn off a/c. Start engine and allow to idle. If temp does not climb and fan does not get called, your cooling system is not the culprit it is your condensor heat adding to the radiator heat load (dirty condensor, filter or low Freon). If temp still climbs idling with a/c off, its the radiator either poor transfer inside (flush and replace coolant) or poor transfer outside (clean from back to front with low pressure spray of water).

I had temp climb to a/c cutout (high normal is 3/4 mark) when climbing hills in overdrive in 103 ambient. So later that night we were checking it all out. Idling without a/c it ran 30 minutes at 12oclock (low normal) and the fan never came on. Tells me radiator is adequate. The a/c did not cutout til it was at that 3/4 mark. If your cutting off before that, it's either poor airflow through the a/c condenser/radiator or low Freon in the a/c, all of which can cause high pressure cutoff at a lower point than normal.
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post #6 of 8 Old 08-27-2017, 03:28 PM Thread Starter
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Thanks for responding guys! The quality of the radiator fluid does look a little iffy. I got a new thermostat, so probably next weekend I’ll dump all the coolant, do a good flush, replace the thermostat, then refill with fresh coolant. I’ll post back with my results! :-)
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post #7 of 8 Old 09-15-2017, 01:27 PM
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If you haven't added an auxiliary cooler for the transmission (assuming automatic) then you might consider adding one. I have the 2011 JKU Rubicon which tended to heat up. Once I added the extra cooler, it has not overheated -despite running offroad in 110 degree temps.
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post #8 of 8 Old 09-19-2017, 09:37 PM Thread Starter
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Well guys, here's an update for ya. I was all set to do the thermostat swap and dump all the fluid. Through my research I found out I need HOAT radiator fluid by the way.
Any way, I was all set to do the work, then one day the radiator fan started shredding the plastic fan grille. So I start tearing into it and I find out that the fan is a generic aftermarket unit. To make it even worse, the motor on the aftermarket unit was a replacement motor that didn't match the fan because at some point I guess the motor that came with the fan packed in. That said, I replaced the fan, motor, fan harness, and grille with stock Mopar items. Through research, I had read about the stock parts failing since they weren't "sealed" units, but I figured it would be good to get a baseline and eliminate any variables in the overheating issue. Taking the old fan out was a bit interesting since the aftermarket unit was physically attached to the radiator via 4 plastic skewers the went through the radiator, the AC condenser and were screwed onto the front side of the radiator. Luckily nothing was broken when the fan started killing itself, and the skewers didn't seem to do anything harmful other than making 4 large holes in to aforementioned parts.
Once I had the old stuff out, it was a simple task to put the new stuff in.

I've now had it in for about a week and no more overheating! I guess the old fan was on it's way out, and wasn't cooling he engine as efficiently as it should have been. As a side note, I spoke with a Jeep tech and he confirmed that on our Wranglers when the computer senses the engine overheating, it kills the AC compressor to reduce the load on the engine, as sort of a precaution to save the engine. So this problem is solved. Since I still have the parts for the thermostat though, I will still replace the old one and do a thorough flush. That way I know it's done, and done right.

Anywho, thanks to everyone who replied with your wonderful suggestions, keep Jeepin'!
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