Overheating from idling too long

[RADuck77]

Hi all,
I tend to ramble, so I'll try to keep it short.
Wife took my jeep to work today so I could drop her truck off at a mechanic shop for an AC repair. Had our daughter pick me up and drop me off at wife's work. Drove the jeep a few miles at slow speed to a doctor's appointment for the wife. I sat in the jeep with it idling for about 30 minutes. AC was on full blast the whole time and blowing cold. Left Dr. office and went to pharmacy, again I sat in jeep with it idling and ac on blast. Suddenly I noticed ac was no longer blowing cold. I didn't think to look at engine temp at this time. I just assumed it would get better when I started moving. Left pharmacy and made it one block and the temp light came on. Then I looked at gage, it was maxed out. Immediately pulled over and shut it off. Looked under hood, reservoir had a little coolant in it, not boiling or anything. Nothing actually seemed hot. Daughter was close by, came and picked us up and we went and rented a car since now it seems we are down to no vehicles. 30 minutes later got back to jeep, started it and scrolled through dash to coolant temp, it was 190, and gage was normal. Kinda unlikely it would go from maxed out on gage to "normal" in 30 minutes. So I am assuming the gage was giving me a faulty reading. Went ahead and drove it home, which is about 35 miles. Watched temp the whole way. It would climb to 208 then drop down to 188, obvious the thermostat is working. Well, so much for keeping it short...
Question is, is this possibly a fluke and will never happen again? Or should I be looking to replace something.

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[Main Line Willys]

did you happen to notice if the fan was running?

 

[sharpsicle]

You might have air in your coolant system.

 

[RADuck77]

did you happen to notice if the fan was running?

I never looked at the fan before shutting it off. When I got back to the jeep and started it, I popped the hood and the fan appeared to be running then. But now that I think of it, would the fan run if it was actually that hot and the engine is shut off? If so, it would have been noticeable when I shut it off.

 

[RADuck77]

You might have air in your coolant system.

Maybe, but it’s never done this before. I’m at almost 50,000 miles. I did crack the reservoir lid a little when it was “hot” and it let out a very small hiss.

 

[DylanM]

Possible air pocket in the cooling system would be my first guess as well.

When you say the reservoir had a little coolant in it, was the level above or below the low mark?

 

[NC_Overland]

I swear my cooling fan works when it wants to. I can pull heavy trailers and not have it heat up at all but in traffic it either stays right at 200 or goes up to 220 and then cools back down. There doesn’t seem to be any rhyme or reason.

 

[Hootbro]

Good suggestions have already been given. I will say though that unless it happens more consistently, going to be hard to nail down.

 

[Alpine Warthog]

My Fan kinda freaks me out when it really starts pulling. It's normally very quiet but those times when it needs to really work it's very noticeable. SO if you never heard it get loud enough to grab your attention, I would check it. I agree it sounds like an air bubble but that fan should have been loud enough to make you look up at some point.

 

[sharpsicle]

Maybe, but it’s never done this before. I’m at almost 50,000 miles. I did crack the reservoir lid a little when it was “hot” and it let out a very small hiss.

That's a true statement before anything happens lol. It's never done it before until it does, and then you go fix it.

 

[RADuck77]

Possible air pocket in the cooling system would be my first guess as well.

When you say the reservoir had a little coolant in it, was the level above or below the low mark?

I assume the low mark is basically the seam, since it says min/max right above it and the min arrow points to it. The coolant in the reservoir was definitely below the min mark and still is this morning with it completely cooled down.
Probably a stupid question, but should I add coolant to get it to between those marks? If so, should that level be checked while hot? Or cold?

 

[Svenable]

Just some thoughts.

If the coolant reservoir has coolant in it when the engine is cold and nobody had the system open before this all started I would be skeptical of air in the system. Where did the air come from? I would think a sticky thermostat but if you were idling and this started after idling the thermostat would already be open. You have a puzzle on your hands.

Things to check are the fan cycling at the correct temperatures, a pressure test of the system to rule out the air in the system or identify the air leak. I would bring the reservoir above the minimum mark while cold and ensure the radiator is full. Check the water pump weep hole for leakage. I would change the thermostat just to be sure, they are cheap. You could pull the temp sender and check it also. A far reach is a collapsed radiator hose but the new style hoses are not really susceptible to this today. Good luck.

 

[DylanM]

I assume the low mark is basically the seam, since it says min/max right above it and the min arrow points to it. The coolant in the reservoir was definitely below the min mark and still is this morning with it completely cooled down.
Probably a stupid question, but should I add coolant to get it to between those marks? If so, should that level be checked while hot? Or cold?

The level should be somewhere between the two marks, checked when cold. If you find yourself having to check the level when hot, it should be no higher than the upper mark.

With the coolant level having dropped, it would be a good idea to give the cooling system a thorough looking over to see if there are any leaks anywhere. Typical leak locations for a lower mileage vehicle like yours are at the reservoir itself and at the plastic connectors of the smaller coolant lines. Air tends to get in the cooling system either when coolant is getting out (leaking), though sometimes it can get pulled in past seals as the system cools.

 

[stevenmicheal]

It could be a fluke, but more likely an intermittent issue with a sensor or the cooling system, so don’t ignore it. Visit a trusted jeep dealership in connecticut where certified mechanics can check coolant level, thermostat, radiator fan, and temperature sensor. If it happens again, it could point to a water pump or sensor problem.
Best to get it diagnosed soon before it turns into a bigger issue.

 

[DylanM]

@stevenmicheal
You do realise the OP lives in Texas, right? Are you suggesting he drives somewhere around 2000 miles with a cooling system problem?

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