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Old 08-30-2011, 01:55 PM   #1
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combination: AC rough idle and overheating

So I did some searching and tried a few things that fixed most peoples problems, but it just isnt fixing mine

I have a 2004 TJ Wrangler X
The problem:
If its a hot day, and I use AC, and I cut the jeep off, and come back to it later before it motor has completely cooled, it will idle rough for a little while and after driving around, it will continue on normal idle.

This happened again and I turned the jeep on and it rough idled horribly to where it almost choked itself out, and AC went warm quick. I turned AC off, and got it to drive to bring it back to normal idle. When I got home, I got the check gauges light and the temp gauge was at 260. I let it cool down, opened reservoir cap, and the coolant was all the way up to the cap.

Previous Fixes:
I flushed the system (garden hose style), old coolant looked fine, and put new coolant in it. When sitting at idle it is fine, you can see that the coolant thermostat would open and close. When I started driving (with AC on) still no problems until I stopped in a parking lot and it would stay at 210 for a lil while, but then noticeably goes to 260 after 4-5 minutes.

I cleaned the IAC for the rough idle, but havent really been driving the jeep to see if it fixed the idle issue.


Is it possible that the coolant thermostat gets weak after continuous heat and ends up staying closed? its the only thing I can come up with

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Old 08-30-2011, 02:59 PM   #2
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did i type too much lol

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Old 08-30-2011, 03:20 PM   #3
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Check if your water pump leaks. It wouldn't hurt to replace your thermostat either.
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Old 08-30-2011, 03:25 PM   #4
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I checked for leaks and found nothing, and I plan on picking up the thermostat tonight and putting it in just to see what happens, can i reuse that gasket for the water pump?
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Old 08-30-2011, 07:23 PM   #5
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something similar to this happened to me on the way to the beach two summers ago. We were goin down the highway and running a/c and it overheated. Well the next day we were driving on the beach and it started to run a little hot then "BAM!" steam going everywhere, cracked the radiator at the top. Turns out the thermostat got stuck and caused it to overheat. (plus im an idiot and did not deflate the tires while riding on the beach lol)
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Old 08-30-2011, 08:46 PM   #6
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Problem continues...

I replaced the thermostat, and it showed the same exact symptoms. Is it possible that my AC compressor is causing the issue? As always when I test for this overheat, I turn AC on while sitting in park, and when it started to overheat again, I turned heat on, while I drove back home. When I got home, the engine was once again sitting at a good temperature, but HEAT still full blast, directional dial was on floor and defrost, and my AC compressors clutch was engaged and spinning. I compared this to a friends car, and when heat is turned on, their clutch would not be spinning.

To make it short...is the clutch on the AC compressor supposed to be engaged when HEAT is on full blast? Could the AC compressor cause my overheating?
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Old 08-30-2011, 08:51 PM   #7
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You say you had yours set to floor/defrost, the defrost uses the a/c compressor to keep moisture out so that would be normal for it to be running. Take a look at the seal on the radiator cap, make sure it is not cracked and is not hard as a rock. For as cheap as they are I'd go get a new cap anyway then trying again
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Old 08-30-2011, 08:55 PM   #8
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Alright, ill get a new radiator cap and reply with good or bad results
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Old 08-30-2011, 10:04 PM   #9
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Problem continues....

replaced radiator cap, and same symptoms. When sitting in park with AC on, it sustains operating temps for about 4-5 minutes, then the needle drastically drops to 260

ANY OTHER IDEAS!? My AC acts up on the rarity, can this still be a cause for overheating?
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Old 08-31-2011, 12:02 AM   #10
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So I did another form of troubleshooting

The temp gauge does this thing, right before it overheats, it will SLOWLY nudge to the edge of the 0 of 210, well right before it overheats I cut off the AC, not even heat is on, and the engine settles back to normal operating temps.

Kept the engine on with no AC for 10+ minutes and the needle never budged past operating temp (lil past 210)

This leads me to believe that it is possible for your AC compressor to overheat your motor...plus, there's is a slight audible grinding noise everytime the clutch engages
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Old 08-31-2011, 11:22 AM   #11
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bump
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Old 08-31-2011, 01:46 PM   #12
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First off, running the a/c makes the radiator/engine cooling system work harder.
Why you ask? Well part of the a/c system is the condenser, and it's job is to take hot freon and cool it. And the condenser sits smack dab in front of the radiator.

Turn on the a/c, the condenser gets hot, and to help cool it the fan is pulling that hot air away from it. Right smack into the radiator that's trying to cool the coolant. So now instead of nice cool air hitting the radiator and being pulled through, it's getting blasted with the hot airflow from the condenser.

Up goes the coolant temp.
The thermostat if it's working, opens further to help flow the coolant faster, if it doesn't the temp climbs.
The rad cap seals the system to raise the boiling point of the coolant, if it doesn't the fluid boils quicker, temp climbs.
The water pump is driving the coolant to the rad to help in cooling. If it's worn or leaking, it's not driving the coolant fast enough and the leak is lowering the boiling point of the coolant, temp goes up.

Then there is the fan, or more specifically the fan clutch. It's got it's own thermostat that controls how much it locks up to drive the fan. Bad clutch/thermostat and the fan doesn't spin fast enough to pull enough air to cool not only the hot freon, but also the hot coolant. Temp goes up.

Restriction in the cooling system, plugged up radiator, pretty simple there. Fluid can't flow the proper amount can't cool properly. Temp goes up.

And don't forget the coolant itself, wrong type doesn't cool as well as the proper will. Temp goes up.

And lets not forget the air temp outside as well, the hotter it is outside, the harder the systems have to work to keep the coolant cool. Any of the above items will raise it's ugly head a lot quicker on a hot day as opposed to a cold one.

While on that, we know that the cooling air stealing a/c condenser is robbing the rad of cool air, but does it have an accomplice? Like that monster winch that's blocking off the whole grill?

And these guys aren't alone. They have evil companions. Like lean running engine, and blocked exhaust and worn out drive belt and his cousin loose drive belt. All can add to overheating. And they have more friends.




OK always start with the basics. Can airflow get to the radiator and condenser.
Make sure the thermostat is working correctly, if in doubt replace it, cheap. Ditto the radiator cap.

Now time to look a little closer
Is that fan clutch working? Is it working correctly? Are you sure?

How bout that water pump, you sometimes have to give more then a quick peek at it.
Crawl under the jeep and look hard at the weep hole for leakage, even use a mirror and flash light to get a good look. They will fool you.
And look at the flow in the rad when the stat opens up. It should be rushing across. If you are seeing a slow meandering flow, you got problems. Stat or weak pump or restriction.

And the only way to check them is to yank em.


As for the rough idle, see above. Those items can cause the fuel rail/injectors to get a lot hotter then they like, and the fuel inside does what it does when it starts getting hotter.
It starts turning into a vapor. Vapor doesn't flow as well as a liquid can, and so the injectors aren't spraying a full load of liquid fuel, so the engine runs rough.
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Old 08-31-2011, 03:10 PM   #13
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Shelby427 has a good solid write up, I agree with everything he wrote. The symptoms you have described in all of your repairs and concerns have indicated it is likely the a/c sytem causing the rough idle and the overheating. It appears the the a/c condensor is not cooling, this could be due to a restriction in the a/c system(likely the condensor), externally blocked/obstructed condensor or poor fan clutch performance. Any of these three problems will cause the high refrigerant pressure to climb past 300-400psi which then overheats the radiator and concurrently adds stress to the compressor which adds stress to the serpintine belt and then stresses the crank shaft causing a rough idle. If the overheat problem goes away when driving on the highway you have a bad fan clutch. If the problem is all the time the condensor may be obstructed, if it is clear you will need the a/c sytem diagnosed by a service profesional.
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Old 08-31-2011, 07:14 PM   #14
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To both Shelby 427 and azwillysjp, thank you so much for the write up! Made my thread "sticky" worthy

It just started to get cool here so I dont drive around with AC and shes driving like a champ. I will eventually get my AC system diagnosed, but I am on a budget nor am I in need of it, but when I do get it looked at and solve, i will post the results to hopefully help someone who might go through this same issue.

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