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Discussion Starter · #1 ·
When letting the JK idle (dunno on-road, she's been parked for a few months, and this issue has me not driving her today when I expected to =) the coolant overflow reservoir fills -completely- to the top and overflows. However, it drains all back down to the normal (between min and max) level as it cools. It doesn't appear to overheat, even when the coolant is spilling out the back, the temp stays right around middle.

Anyone heard of this? I was thinking the line from the overflow is clogged as there appears to be a small leak where the line meets the radiator cap, but then it wouldn't drain back as it cools? Is there a lower line I don't see?

Thanks!

!c
 

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I would have the radiator cap checked...pep boys might check them.......if thats okay i would compression test the motor........usally radiator fluid getting that much pressior is not good.........good luck
Used to check the radiator for emissions with a sniffer-if u got a reading pretty much head gasket time. Maybe a bad/sticking thermostat?...good luck and keep us posted on what u find.

Is this thing on......?
 

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Discussion Starter · #3 ·
Sweet, thanks for the advice! I just replaced the radiator cap and the overflow line (about $10 in parts total), and so far so good - she's holding at just below half temp idling, and hasn't backed up yet. I'll give it another 10 minutes, and if no back-up, good to go.

!c
 

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Discussion Starter · #4 ·
No such luck - just a few minutes ago I got to watch it happen, everything was fine and then out of the blue, you could hear a rumbling, and then the reservoir filled up again- bubbling and boiling like some witches brew... =(

Guess I'll be taking her to the shop! I looked for any obvious coolant leaks anywhere, like around the water pump, but none to be found. No water in the oil, fortunately.

!c
 

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Discussion Starter · #5 ·
Well, she's back from the shop. Turns out the problem was just downright dumb (on my part). Some time ago I added a bypass relay to the fan to prevent it from coming on in water. Late last summer, right after I retired the JK as my daily driver, the TIPM went out and during diagnosis of the problem, I removed pretty much all custom wiring and re-set it to stock, or so I thought. Turns out I left the low speed control on the fan disconnected. It had no low speed =(

No other issues with the engine.

Didn't take 2.5 weeks to figure that out though *grin* While she was in there, I had the 5.13's I had sitting around installed, true-trac's front and rear, and new balljoints put in. =)

!c
 

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Discussion Starter · #6 ·
Went from great to worst yesterday. *sigh*

Everything all back together, just waiting on my new axle shafts to come in, beautiful weather out, figured I'd take her out to get the inspection done.

Strangely, on the freeway, I was running way cold. Like 1/4 on the temp gauge.

Got off the freeway, and she slowly climbed back up to the mid-point.

While I'm waiting in the shop, I hear a loud noise and a hiss coming from the bay. I look out there, and my jeep is lost in a cloud of vapor.

The radiator blew out on the driver's side. Now, she's waiting to get towed in again.

I'm about ready to sell this f*****g thing.

!c
 

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Discussion Starter · #7 ·
Ok, root cause of the problems finally determined: the temp sensor was malfunctioning, but the PCM reported it as functioning properly. It wouldn't register more than 140 degrees - no matter how hot the coolant was. IR thermometer measured 240 when the PCM registered 140.

Seems to be ok now, after a new radiator, new thermostate, new temp sensor, new hoses, etc. etc.

!c
 

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Your not alone, I see a lot of cooling issues with JK's in Vegas.

The JK uses a typical negative thermister ECT which sends a signal to the ECM which transmits the coolant temp through the can bus for use by the instrument panel, HVAC, fans, etc. The stock ECT sensor is made of plastic and easily damaged if overtightened so be careful.

The TIPM is responsible to activate the fans based on coolant tempreture and condenser pressure. The low speed fan relay is in the TIPM and HS fan relay on the core support.

All JK owners should do themselves a favor to address cooling problems.

One, install a real ECT gauge, the stock gauge is as useful as a light IMO. Better yet get a scan gauge so you can look at other stuff and some have audible alarms. The stock gauge will stay near center over a wide temp range and may not warn you until it is too late. ECT is so important off road and you really need reliable feedback.

Two, the TIPM is not always reliable, especially with a V8 or when it is exposed to high temps. The connectors in the bottom can also be problematic.

You can easily install a HS fan bypass by tapping one wire into the HS fan relay and running it into the cab in times of emergency.
 

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re: 2 + year old "Coolant Backing Up "Post

Your not alone, I see a lot of cooling issues with JK's in Vegas.

The JK uses a typical negative thermister ECT which sends a signal to the ECM which transmits the coolant temp through the can bus for use by the instrument panel, HVAC, fans, etc. The stock ECT sensor is made of plastic and easily damaged if overtightened so be careful.

The TIPM is responsible to activate the fans based on coolant tempreture and condenser pressure. The low speed fan relay is in the TIPM and HS fan relay on the core support.

All JK owners should do themselves a favor to address cooling problems.

One, install a real ECT gauge, the stock gauge is as useful as a light IMO. Better yet get a scan gauge so you can look at other stuff and some have audible alarms. The stock gauge will stay near center over a wide temp range and may not warn you until it is too late. ECT is so important off road and you really need reliable feedback.

Two, the TIPM is not always reliable, especially with a V8 or when it is exposed to high temps. The connectors in the bottom can also be problematic.

You can easily install a HS fan bypass by tapping one wire into the HS fan relay and running it into the cab in times of emergency.

I know it's quite a few years since this reply was submitted by you , MoTech but I also know you're an active regular contributor to the forum ( i subscrb to your LS thread ) so figured I'd ask after hearing you say that you guys see many things centering around the JKs and ECT sensor ; I've noticed no outstanding temps via my use of a Flashpaq's diagnostics to check tennis if the engine coolant ( it read - 30 C or basically normal if "k=0" IOWs the thing didn't detect any upswing in resistance and it's normal and doings its job but i have recently noticed s small collection of the HOAT gathered in the channel recess surrounding the ETC Sensor hole . I wipe it off and by end of drive its back with the residual anti freeze . coukd overfilled antifreeze result in this or (& I was wary of any stress when doing so to a plastic part from Chrysler ) I did ensure it was tightened to right amount so wondering if a 2011 3.8l is just needing a new , upgraded , metal sensor or do I have bigger issues ? is this a simple swap as far as removal and install of replacement and what would you recommend ?
here is the collection I refer to on my engine





thanks if you have time to gimme a little of your knowledge on this ... oh, my coolant may be just slightly overfilled so maybe splash back ?)
 
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