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samanthamae

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EDITED TO ADD: after replacing the radiator cap, the engine light came on later that day while I was driving and the code it gave us was "Engine coolant not getting to operating temperature"
My 2010 Jeep Wrangler Unlimited Sahara with 92k miles began overheating a little over a month ago. Thankfully, I was close to home when it happened and was able to make it back before it reached the H completely. We started by replacing the thermostat which didn't solve anything, so we replaced the water pump as well and flushed the radiator. Still, it was overheating and losing coolant - but the overflow tank still had the same amount of coolant in it. **also before anyone asks, yes we did burp it and make sure there was no air after every time we refilled the coolant** Because the overflow was pretty full still, we replaced the radiator cap. After doing this, I was sure it was fixed as I was able to drive it for about a week and a half without losing coolant. However, a couple of days ago I went to the grocery store about 10min from our house and on my way back, the engine began overheating again. I immediately turned off the AC, rolled the windows down, and put the heat on full blast so that I could make it back to the house somewhat safely. The air that came out when I turned the heat on was pretty cool despite having my heat set as high as it will go. Every now and then on the short drive back, the heat would get hot for a few seconds then go back to being cool. When it cooled off later that day, I checked and there was no coolant in the radiator or in the overflow tank. Does anyone have an idea of what it could be or what we could try next? There are no signs/symptoms of a leak, no coolant in the oil, and the fans work. I have seen somewhere that to ensure there is no air in it with some of the 2000's Jeeps, you have to replace the coolant with the front of the Jeep on a slight incline - so we are trying that next. Anyone who had the same issue and was able to fix it - please let me know. I feel like we've tried just about everything!
 
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BLACKJKU

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It's it's easier to get the air out when the front of the Jeep is jacked up so the air will go to the highest place. Is your cooling fan running when it's getting hot?

Does it only do this when the AC is on?
 
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samanthamae

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Yes the fan does run when it gets hot. When we have been working on it, we leave it running to see if it will overheat and we rev it to see if it will overheat - but not with the AC on. When I've been driving it (because I thought it may be fixed), yes I have had the AC on. Now that you ask, perhaps we should have had the AC running while testing it!
 

BLACKJKU

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The AC will make it overheat faster, I think the fan has 2 speeds and is to run faster when the AC is on.

I would try burping again with the front jacked up just to be sure there is no air in the system.
 

kk2010jk

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Is your Oil ok, not milky?
Head gasket allowing air to be pumped into the cooling system?
I think of cooler heater air as thermo stuck wide open. There could be air pockets still there. I bought for my previous car a Uview airlift system that minimalized trapping air while refilling the cooling system. These modern closed systems are a bear to flush and refill
 
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samanthamae

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Is your Oil ok, not milky?
Head gasket allowing air to be pumped into the cooling system?
I think of cooler heater air as thermo stuck wide open. There could be air pockets still there. I bought for my previous car a Uview airlift system that minimalized trapping air while refilling the cooling system. These modern closed systems are a bear to flush and refill
Yes the oil looks great. I’ll have to look at the thermostat later today when I have a chance, but we just replaced it. But still - it is completely possible that it’s stuck open!
 

Anybodyhome

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My concern is the loss of coolant with no visible evidence (no big, green puddles on the ground). Typically, if the water pump is shot, the thermostat stuck; it may overheat, but you don't lose coolant.
Clearly, the condition is such that it's cooking enough to evaporate the coolant, right? If you experience the unmistakable smell of cooking coolant, I'd be concerned the coolant is cooking off on the head somewhere.
 
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samanthamae

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My concern is the loss of coolant with no visible evidence (no big, green puddles on the ground). Typically, if the water pump is shot, the thermostat stuck; it may overheat, but you don't lose coolant.
Clearly, the condition is such that it's cooking enough to evaporate the coolant, right? If you experience the unmistakable smell of cooking coolant, I'd be concerned the coolant is cooking off on the head somewhere.
That’s been my concern as well. The only problem is we haven’t smelled anything and haven’t had any smoke or noticeable exhaust. But I feel like it HAS to be cooking somehow because the coolant literally disappears and we haven’t found any leaks whatsoever.
 

Anybodyhome

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If the temp gauge is all over the map while you're driving- goes up & down seemingly without reason- that's a sure sign there's air in the system.

Are you refilling coolant via the reservoir or the radiator directly? I would suggest filling the reservoir to its cool level before driving anywhere after it's sat for a while. Then open the radiator and fill it directly, little at a time so the coolant forces the air back out of the radiator- pour, let it settle, wait for the burp- repeat as necessary. But I think you said you've done that already.

By the way, did you replace the t-stat with a true OEM or a different one?
 
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SteveF

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Not sure about the t-stats in jersey but is it possible that the stat is upside down?
 

Anybodyhome

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Not sure about the t-stats in jersey but is it possible that the stat is upside down?
The best, and most common way to buy a JK t-stat is with the housing. There's virtually no way to install the t-stat within the housing upside down or backwards.

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mrjp

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If you have a bad head gasket you can pressure the cooling system and blow coolant out the overflow. I would test what ever coolant is left in the system if possible