My Jeep is Overheating at Idle

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SwampSurvivor

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00 Cherokee 4.0 , auto trans. 214k miles. Mostly a trail vehicle at this point.

Something new this year. It's been gradually getting worse but now it's to the point that I can't let it idle, even with the electric fan wired ON all the time. My last off road trip I noticed that when it started to heat up, I had no heat coming out of the vents. Once I bumped up the idle I got heat and the temperature dropped down again.

When it started earlier this year it would run at 225 on the highway and creep up to 235 sitting. If I beat on it - which happens a lot - it would heat right up to 235 or so and not come back down until I shut it off and let it sit a while with the electric fan running. Usually I can get on it pretty hard and never crack 210 or 220.

So I changed out the fan clutch for a new HD fan clutch that I've used in the past. When I have used this in the past, it didn't matter how hard I beat on the thing, it would never go above 210. The new fan clutch is just as loud as the other HD ones I have had, so the fan clutch is good and moves a ton of air. The fan clutch did help a bit, though, as it runs on the highway at 210 now. But as soon as I let it idle, it creeps right up.

I had it running in the yard the other day to winch some stuff around , with the electric fan running too and it heated right up to 230. Ran the idle up a bit and the temperature dropped off to a normal level.

I'm thinking water pump? Thermostat, radiator, hoses, fan clutch are all 3 years old at most. Water pump I changed back in 2012 maybe 45K miles ago. Due to having to replace the upper radiator hose every year, it has has more than it's fair share of coolant changes and flushes.

Hoping it's not the head that cracked but I imagine it would do it more under load than sitting idle.
 
I would at least pull the water pump and take a look at the impeller. It sounds like it may be eroded away, especially since you say you had to raise the RPM to get any heat out of it. That could also be a clogged heater core too but since you are over heating at idle that's the first place I'd look.

Does your radiator flow enough coolant? Have you ever flushed it out?
 
Have you done something as simple as to thoroughly flush out the external fins of the radiator? It happened to my Sierra.... 20 years of dirt, chaff, bug exoskeletons and everything else... slowly starved the radiator of air flow. And it overheated the quickest... at idle.

And when it can't flow air the way it was designed to... it overheats.

Don't know... but it is soemthing quick and cheap to try.
 
Coolant is at the proper level, right? I only say that because I've experienced your two symptoms together (overheating, no heat out of the vents even with heater on) and I simply had low coolant due to a leaky hose.

Otherwise, the fact that getting the revs up, even when not moving, brings the temp down points to a flow problem. If you've replaced everything else besides the water pump, then it's probably the water pump.
 
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Since you have been in the cooling system so much.. have you ruled out air pocket?

A properly functioning radiator cap is critical to the proper operation/function of an "open type" cooling system. The open cooling system rad cap has 2 valves and 3 sealing surfaces and again, all must function correctly and the entire cooling system must be leak free. The bottle and rad cap allow both coolant and any air to escape from the rad/cooling system as the motor heats up. Only coolant is allowed to return to the rad/cooling system as the motor cools.
 
If the radiator has not been cleaned or replaced in a while, that's the first thing I would check. My 1994 Ranger would creep to the top of the safe range when sitting at idle when I first got it. The radiator was clogged internally and externally due to neglect and being off roaded a lot without getting cleaned afterwards. A new radiator put it back to the middle of the normal range.
 
I spray the fins of the radiator out every few off roading trips. Plus it's only a few years old.

I think I'll take everything apart this weekend. It's not too terribly hard to pull the water pump out. I was thinking about getting a HV pump but I've read mixed reviews on them. So regular it is.


Originally Posted by Chris142
Is the fan clutch actually locking up and making the fan scream? We stopped using Hayden fan clutches because they have a huge return rate now.


It passed the pencil test! Snapped it right off at idle.
Originally Posted by krismoriah72
Since you have been in the cooling system so much.. have you ruled out air pocket?

A properly functioning radiator cap is critical to the proper operation/function of an "open type" cooling system. The open cooling system rad cap has 2 valves and 3 sealing surfaces and again, all must function correctly and the entire cooling system must be leak free. The bottle and rad cap allow both coolant and any air to escape from the rad/cooling system as the motor heats up. Only coolant is allowed to return to the rad/cooling system as the motor cools.


Cap is new , forgot to list that as new. I operate it at pretty extreme angles (and on it's side once in a while), any air bubbles should get burped easy.
 
Xj's run hot. Did you put a better radiator in it when you replaced it or just a factory replacement? I'd think it's a radiator problem, possibly a coolant flow problem but hard to tell. I don't like that you said you didn't get heat out of the vents when it was running that hot though. I'd do some investigating, make sure you don't have combustion getting into the cooling system and getting trapped in the heater core. Many 4l with cracked heads drive just fine.
 
Back flushing radiator and system, spritzing dirt out of fins may help. test cap. Stock thermostat on my Jeep /carbed AMC 360 V8 opened at 195' 235' seems too high to me. Original Water pump? 2nd? impeller could be eroded generic iron case water pump experience not 4.0 specific, Checking for bad HG done by pulling plugs .A clean plug is a leak. When it is running can you smell coolant in exhaust? Do the flushes and cheep stuff first. I wouldn't use a pressure tester on a 215 K Mile cooling system . You may discover a proof of the Heisenberg Uncertainty Principle .
grin2.gif
 
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Once owned a 01...... don't remember if the water pump had a plastic impeller or a metal one. The plastic ones were prone to "bugging up" where the metal nut attached to the pump. Would go with that being bad. Other than that, I'm sure you already checked the quality of the coolant and observed the flow through the radiator .........pumps easy to check and truthfully, if it's the original, replace it anyhow. Good luck...

Ok. See you replaced it before....still look into the impeller. That's my diagnosis, and I'm sticking to it!
 
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Chris142 I'm guessing the " pencil test " is similar to " rolled up newspaper test . If the clutch is locking up it breaks the pencil .
 
Before throwing any more parts at it I'd get both the engine and cooling system compression tested.
 
Originally Posted by Chris142
What's the pencil test?

Stick a pencil in the fan. If it breaks, clutch is good.
 
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