Jeep Garage  - Jeep Forum banner

1 - 12 of 12 Posts

·
Registered
Joined
·
11 Posts
Discussion Starter #1
My daughters 2004 Grand Cherokee (4.0) a week ago Friday threw a code - said Thermostat, so I replaced the thermostat, OEM 195, easy job. Drives for a week all is fine. Last Friday it overheats - she has it towed to my house. No leaks, system is full, pressurized, all looks fine. When she bought the car 3 yrs ago it was loaded with stop leak, which I told her was a big concern but it was too late. But that was 3 yrs ago and it's been fine. My first thought is that when I changed the t-stat and replaced a lot of coolant that it stirred stuff up inside and maybe the t-stat was stuck. Took it out, looked fine, put it in water, heated, it opens fine, etc, cabin is smokin hot, etc. Reinstalled t-stat, new gasket. On to plan B - radiator, was original, and with all the stop leak thinking ok that has to be clogged and the problem. Replaced it yesterday, refilled the system again, still overheating. Water pump is only item left , showing no signs of being bad, not weeping, pulley is true, no noise, but replaced it anyway. Refill again, STILL overheating. UUUUGGHHHH......

I do not think it's a head gasket as shows none of the expected signs such as exhaust vapor, no coolant in the oil (its clean), no oil found leaking, idles fine, starts fine. Not likely a temp sensor as that would throw a code and there are no codes. Now - the only thing I've noticed is that the electric fan doesn't seem to be turning on until it's pretty hot past the 195 -210 operating range, and I don't know if the fan is functioning at full capacity as it's not my car, but the fan is essential to cool if just sitting idling but would that alone cause an overheat? There's nothing left as there are not that many moving parts to a cooling system. Again for the past 3 yrs the car has been fine - no issues, and even a week after t stat change.

Would REALYY APPRECIATE and insight here as I'm at wits end on this one. The only good news is it's easy to work on, but I'm tired of working on it.

THANKS!
 

·
Registered
Joined
·
1,097 Posts
First off 4.0's with mileage typically run hot especially in hot weather at idle.
210 deg. is not that unusual in hot weather especially when idling for long periods but at that temp the efan should be running.
New water pump..check.
New radiator..check
New thermostat..check
Temp sensor....?

Is it only the temp gauge that indicates overheating or are there other indications like rough idle, etc?
What do you exactly mean the efan is too cool?
After you replaced the thermostat, did you burp the coolant system, important?
Any coolant loss in the coolant reservoir?
Does the efan 'always' turn on when the AC is enabled or when the temp approaches or exceeds 210 deg.?
What about the main radiator clutch fan? Did you test it?

Might want to have a coolant pressure test to absolutely verify no leaks or air (bubbles) getting into the system.
They're quick and relatively cheap.

Based on what you've said, next thing i'd do after all of the above is a complete coolant flush making sure the coolant system is burped properly.
The coolant passages in the head and block could be clogged with stop leak.
I would never recommend using that stuff but instead fix the root cause of the leak.
 

·
Registered
Joined
·
11 Posts
Discussion Starter #3
Thanks @moparado . Pressure test makes sense. Yes also thought that the stop leak may have clogged a passage or two as this only occurred a week after changing the T stat . Agree 100% that stuff shoudln't be used and tried to warn them not to buy it when I learned it was in the radiator. If there is a proper way to burp the system please advise. I parket it uphill with the cap off and let it run until it stopped spewing out the filler neck. Any other thoughts are appreciated. I'll check at what tempp the fan in engaging too
 

·
Registered
Joined
·
1,097 Posts
The radiator fans on these Jeeps vary.
What fan system does yours have?...... clutch/efan combo, efan(s) only, hydraulic fan, etc.
Are the fan shroud(s) in good order?
Burping after a complete coolant flush is important.
Sounds like you probably did it right.
The only thing i'll add is make sure the heater is on full heat when doing the burping procedure.
You might want to search Utube videos to make sure its done correctly.

The stop leak could very well have clogged some coolant passages in the block and heads.
Its not clear, did you do a complete coolant flush or just add more coolant after the water pump and radiator replacements?

I've been through about same routine with my 4.0.
Replaced every thing in the coolant system including an upgraded heavy duty clutch fan yet it still ran hot at idle or stop 'n go traffic especially in hot weather. Worst was waiting in slow fast food drive thru's.

When my auxiliary fan finally came on, it did start cooling or at least stabilize further thermal rise.
In my case the efan came on too late to do any good.
So the efan was the 'key' to solving the problem.

My solution was to jury rig my auxiliary efan with an over ride switch with a 5 minute on timer.
When i see the temp starting to rise, i just press the over ride switch, efan turns on unconditionally for 5 minutes.
During those 5 minutes at hot idle, the efan will reduce the temp from 210+ deg to the thermostat temp spec.

I've also had heat soak problems where i'd park my Jeep with hot engine, run into a convenience store for 10 minutes and then when i started the engine it was hard to start, misfiring in hot weather.
A similar thing to vapor lock with carburetor'd engines because the exhaust manifold is directly under the intake manifold, near the fuel injectors and fuel line.
With my 5 minute over ride switch, i enable it immediately after shutting down the engine.

Both heat related problems solved.
 

·
Registered
Joined
·
11 Posts
Discussion Starter #5
@moparado - thanks much. This Jeep has efan only which I’ve seen as correct for 04 I believe. Now it’s not coming on at all so that’s next. It was engaging earlier so I’m not convinced that’s the entire issue but when not engaging at all it has to be swapped. Will take the shroud out again and see if I can hot wire it to see if it runs or if just a connection . I don’t know what speed it should run at so not sure how to know if it’s 100%. When burping I didn’t have heat on full so can do that again too for what it’s worth but the cabin gets way hot when I’ve done it level ground with heat on full so doubtful will be difference . No heater core blockage issues are present. Fan is the only other variable at present other than something clogged internally. Other fill have been only refills - drain radiator- swap part- refill. But done that at least 8-10 times over the course of this as also did radiator flush liquid and then drained 3-4 times after to get all that out . Gallons of coolant have gone though this thing after so many steps . I’ve not done a good old fashioned reverse flush like on old cars where you install a flush kit into the heater hose and connect the garden hose and the flush tee on the radiator. Haven’t done one of those in ages
 

·
Registered
Joined
·
1,097 Posts
Ok so only an efan.
Depending on the Jeep some have variable speed efans controlled likely by the PCM.
If your Jeep does have a variable speed efan that could complicate trouble shooting.

I'd observe the efan operation from a cold start to hot idle to verify if its operating properly.
See if it starts spinning slow then faster as the engine heats up towards 210+ deg.
Without being there and based on all thats been said, i'd start focusing on that efan assuming the flush and burp were properly done.
Also turn the AC on when the engine is warm/hot as a test to determine if the efan runs at all and if it starts cooling things down. The fan typically should turn on even with a cold engine when the AC is turned on.

Could be the efan itself, its relay, in the case of a variable speed efan - the controller or the temp sensor are all suspects.
By the way the temp sensor is extremely easy to replace on these 4.0's.

FYI, my 2K XJ's 4.0 auxiliary efan is non-variable speed, its either full on or full off.
The radiator cooling on it includes a clutch fan and an efan which turns on only when things get hot or the AC is enabled.
But as i mentioned the efan turns on way too late on my 4.o to do any good once the temp rises much over 210 deg.

Maybe someone here knows exactly what efan system you have on your '04 GC 4.0.
 

·
Registered
Joined
·
11 Posts
Discussion Starter #7
@moparado / thanks much. When u say the temp sensor is easy to replace - which temp sensor are you referring to? The one on the tstat housing or another? Tried to Hotwire the fan tonight after removing the shroud again . Ran for about 10 seconds then quit and couldn’t get it to run again . I plan on replacing tomorrow. Some fan has to be running even at idle to keep air moving through the radiator so this has to be a factor . If I can’t get it to run with straight jumps to the battery and ground, that would seem to rule out the relays. Really appreciate your input. Let me know about the sensor- if a fan sensor where is it located? I like easy 😊
 

·
Registered
Joined
·
1,097 Posts
@moparado / thanks much. When u say the temp sensor is easy to replace - which temp sensor are you referring to? The one on the tstat housing or another?
Before hot wiring the fan, did you try the AC-on test i suggested?

The older generation of 4.0's had two temp sensors, one located near the water pump and the other located at the rear of the engine somewhere i believe for the temp gauge only.

The later 4.0's at least with one speed fans had only one temp sensor located at the front of the engine near thermostat housing.
My 2K 4.0 has only the one located at the front of the engine and unless they changed things the next 4 years i'd think you only have the one in front unless......

If you have a later variable speed fan then its possible there's another dedicated fan sensor somewhere probably in or on the radiator itself.
Typically after market variable speed fans use a temp sensor that mounts in or on the radiator somewhere.
Don't if Jeep did similar but is there a wire harness going directly on the radiator somewhere?
If so, then that would be the sensor that controls fan speed.
If no wiring to the radiator then its possible the PCM is relying on the main temp sensor at the water pump.
Again if i had a schematic, i could verify exactly whats going on.

There's a good chance your Jeep has a variable speed fan since its the only cooling fan.
If it is a variable speed the PCM is controling the fan speed via a sensor, possibly a module and a relay(s).

Does the fan connector have two or three contacts?
Did a quick search on RockAuto where they show fans with 2 and 3 wire connectors.
The 3 wire fan's motor could have two field windings to control a low and high fan speed.
The 2 wire fan for a variable speed would need a controller module to change speeds or either its an on/off fan.

In any case there has to be a fan relay or maybe two somewhere.
 

·
Registered
Joined
·
11 Posts
Discussion Starter #9
Connection is a 3 contact . Pigtail right off the shroud to the left plugs in to connection. My understanding is 2 speed. Hotwiring got it to run once for about 10 seconds . Couldn’t get it to run again . Just got home with replacement. Will be EZ install. Will advise later tonight!
 

·
Registered
Joined
·
11 Posts
Discussion Starter #10
Problem solved. We missed the obvious up front. Issue was the fan. replaced today with new Dorman assembly - super simple - plug & play, and all is well. I missed that regardless of all the other components if there's no air movement through the radiator the car will overheat. Of course. It didn't occur to me until after the water pump. Not knowing the vehicle I didn't know the fan or if / when it runs etc. So my daughter has a COMPLETELY new cooling system of thermostat, housing, radiator, cap, water pump, and fan. Should be good for a while. All in parts total is only about $290, and all with lifetime warranties. Interestingly learned also that the fan is connected somehow to the AC working well as when this was going on the AC would only start to cool then shut down and blow warm. With this fixed it runs fine now. Really have to say that this 04 Grand Cherokee with the 4.0 is a pleasure to work on compared to SO many other vehicles as everything is easy to get to which makes a HUGE difference.

Thanks so much for the traffic @moparado . Hopefully this will help someone else with a similar issue.
 

·
Registered
Joined
·
11 Posts
Discussion Starter #11
UPDATE - While early in the process the fan was occassionally on it seemed in my opinion to be running slowly , but as not my car I wasn't sure. Later on it was noticed as NOT running when it should have been which was a clue. At a certain temp it shoudl come on always and it wasn't. My advice is in a cooling system issue always check to make sure the fan is engaging at the correct time throughout the process.
 

·
The beast from Brazil
Joined
·
8,246 Posts
The 2004 Grand Cherokee should have two control relays in the PDC to control the cooling fan at low or high speed.The relays are controlled by the PCM. Before 2004 models have a pulse width modulated relay under the right head light.
 
1 - 12 of 12 Posts
Top