Overheating at idle: next steps?

Sea Cot

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I'm chasing an overheating at idle problem that first appeared this April. General info: 2006 LJR, stock 4.0L, 168k miles. New parts installed at 161k miles: Mopar radiator, t-stat, heater core, all 4 heater and radiator hoses, radiator cap.

The first overheating incident happened this April during a trail run. While idling at the side of the road for ~10min, the temp gauge was pegged at 260. I estimate it was running at this temp 5 min or less. There were no obvious signs of trouble/damage after this incident. 1/2 gallon was needed to top it off and burp the system. I could see water flowing and the top hose was firm feeling. Didn't have any leaks or other problems since. . . . but in fairness I've probably driven the Jeep 10 days since April. Damn rain.

After a Sunday drive this week, I decided to decarbonize the cylinder head with water. Everything was going fine until, , . I noticed the coolant in the overflow tank was boiling. Great. So I shut 'er down, then used a towel to crack open (not completely remove) the radiator cap to release steam, relieve pressure. I eventually removed the cap and found a few pieces of rubber gasket shrapnel which peaked my curiosity.

I picked up a new fan clutch since I had two overheat at idle situations. Before diving in for the R&R, I decided to fill and pressure test the cooling system. I used an airlift tool to fill the coolant. When I pressure tested the system, an air leak was discovered between the radiator top tank and core. The radiator is under warranty, so I'll deal with that this week. I still had the old Mopar radiator that came in the Jeep. I flushed the old radiator 'til the water ran clear. Nothing sketchy came out. I installed the new fan clutch, old radiator, airlift filled the coolant, then pressure tested the system. It held steady at 14#.

The test drive was ~8 mile round trip to the quarter car wash to rinse off the engine. No sweet smell from the exhaust, no drips, no leaks. At operating temp the gauge read ~215* and stayed there while driving. When I pulled in to the car wash lot the needle climbed instantly. I shut it off before the needle reached the red zone. Driving home the temp stayed at 215 while air was moving. When I got home I let it idle to see what'd happen. In less than 5min the needle hit red and the check gauges light came on. So, I pulled into the garage, shut 'er down, and jumped on the www.

The next things I'm planning to do are go all-in on flushing the system (Prestone flush & clean, pull t-stat, pull block drain plug), until the new warranty replacement radiator arrives. I expect to be done flushing once the replacement radiator arrives so that I can install a new t-stat and I can verify the proper amount and concentration of coolant is filled. I'm hoping/expecting this is a small problem, but time will tell. What say the WTJF crowd?
 
I'm chasing an overheating at idle problem that first appeared this April. General info: 2006 LJR, stock 4.0L, 168k miles. New parts installed at 161k miles: Mopar radiator, t-stat, heater core, all 4 heater and radiator hoses, radiator cap.

The first overheating incident happened this April during a trail run. While idling at the side of the road for ~10min, the temp gauge was pegged at 260. I estimate it was running at this temp 5 min or less. There were no obvious signs of trouble/damage after this incident. 1/2 gallon was needed to top it off and burp the system. I could see water flowing and the top hose was firm feeling. Didn't have any leaks or other problems since. . . . but in fairness I've probably driven the Jeep 10 days since April. Damn rain.

After a Sunday drive this week, I decided to decarbonize the cylinder head with water. Everything was going fine until, , . I noticed the coolant in the overflow tank was boiling. Great. So I shut 'er down, then used a towel to crack open (not completely remove) the radiator cap to release steam, relieve pressure. I eventually removed the cap and found a few pieces of rubber gasket shrapnel which peaked my curiosity.

I picked up a new fan clutch since I had two overheat at idle situations. Before diving in for the R&R, I decided to fill and pressure test the cooling system. I used an airlift tool to fill the coolant. When I pressure tested the system, an air leak was discovered between the radiator top tank and core. The radiator is under warranty, so I'll deal with that this week. I still had the old Mopar radiator that came in the Jeep. I flushed the old radiator 'til the water ran clear. Nothing sketchy came out. I installed the new fan clutch, old radiator, airlift filled the coolant, then pressure tested the system. It held steady at 14#.

The test drive was ~8 mile round trip to the quarter car wash to rinse off the engine. No sweet smell from the exhaust, no drips, no leaks. At operating temp the gauge read ~215* and stayed there while driving. When I pulled in to the car wash lot the needle climbed instantly. I shut it off before the needle reached the red zone. Driving home the temp stayed at 215 while air was moving. When I got home I let it idle to see what'd happen. In less than 5min the needle hit red and the check gauges light came on. So, I pulled into the garage, shut 'er down, and jumped on the www.

The next things I'm planning to do are go all-in on flushing the system (Prestone flush & clean, pull t-stat, pull block drain plug), until the new warranty replacement radiator arrives. I expect to be done flushing once the replacement radiator arrives so that I can install a new t-stat and I can verify the proper amount and concentration of coolant is filled. I'm hoping/expecting this is a small problem, but time will tell. What say the WTJF crowd?
Did you replace the water pump? That’s the one component you failed to mention replacing. I would also drain the block and flush with distilled then start off with fresh 50/50 zerex.
 
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Does the fan roar when it gets hot? Is it just a bad temp sensor? Have you changed the radiator cap? As @Chris says I'd be careful with the thermostat, I got a dud recently. All good advice, I just pick cheap easy first.
 
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Overheating at idle or very low vehicle speeds is usually an airflow problem. Since a new fan clutch has been installed, severely clogged radiator fins or a/c condenser fins might be a place to look. Overheating at speed usually indicates a coolant flow problem, so in this case the water pump and thermostat would seem to be ok.

Is the fan shroud in place? When the overheating is occurring does the fan roar noticeably when the engine is revved, indicating that the new fan clutch has fully engaged?
 
It sounds like it is hot if you are seeing it boil in the overflow tank. Did you check the coolant properties? I’ve got my radiator in the shop being rodded and pressure check for the same reason. I have a 16# cap on it and the radiator shop guy said I should have an 18# put a 13# on it. I’ve gone thru and overhauled my system so I know what I’ve got going forward. Kansas gets too hot to mess around with this type of issue. Make sure the condenser is clear.
 
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It sounds like it is hot if you are seeing it boil in the overflow tank. Did you check the coolant properties? I’ve got my radiator in the shop being rodded and pressure check for the same reason. I have a 16# cap on it and the radiator shop guy said I should have an 18# put a 13# on it.
18 lb. is correct for the TJ.
 
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18 lb. is correct for the TJ.

I just read the system review in the manuals. Designed at 14-18psi. I currently have a 16# so I will purchase a 18# today. On a good note, my radiator is clean and no issues. It is not OEM and is a generic for the jeep product. I have an MT and this radiator has ports for AT. He did say the cooling lines were actually larger on this radiator than an OEM which is a little surprising to me. I'm not sure how that will affect the system, but not worried about it either. Its clean, and will transfer heat. Now to find a Stant cap in town.
 
Thermostat: Hasn't been ruled out completely, but it seems to be working. Regardless it'll get replaced for peace of mind/cheap insurance.

Water pump has not been replaced, but is verified working via seeing water flows, feeling hoses.

Not sure about "roar" sound, new fan clutch seems to be pulling more air than old so I'd say the roar is restored. The cap was replaced >3yrs, 7k miles ago. It'll also get replaced for peace of mind/cheap insurance.

The current/old radiator was flushed clean, blown out with compressed air prior to install. The OEM shroud is intact.

I don't have a refractometer, or other tester, to test coolant properties. The coolant has been mixed- yellow G05 and green "standard" stuff.

I washed the condenser, but didn't blow it out when I had the radiator out. So, looks like I'll add that to the list.

Another variable in this is I have a Xeon 8-S mounted on a Warn mounting plate. The system is covering a fair amount of real estate, so it might be a contributing factor but not necessarily the main cause for the problem?
 
A winch won't affect cooling, unless the radiator is marginal and on the verge of overheating when anything like a new dead bug on the front of the radiator would cause it to overheat. Keep in mind that we're still looking for a good aftermarket radiator that cools as well as the Mopar. Store brands and cheap online brands definitely don't, it takes an expensive aftermarket to do as well.
 
…Another variable in this is I have a Xeon 8-S mounted on a Warn mounting plate. The system is covering a fair amount of real estate, so it might be a contributing factor but not necessarily the main cause for the problem?
If you haven’t had this before and the winch was there, I doubt that’s the issue. Run hotter, a little maybe, but not to an OH condition.
 
Last night I drained the coolant and then filled with a bottle of Prestone flush & clean and distilled water. Brought 'er up to operating temperature, drove around, then let it idle in the driveway. The gauge stayed steady at 210. Today I drove around for around an hour, and again no issues. Tomorrow I'll put more time & miles on the flush brine, then drain it, and fill with a proper coolant mix.