[RESOLVED] Overheating issues: Out of ideas

InfamousCanadian

TJ Enthusiast
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Jan 10, 2019
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137
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Canada
Hi everyone. I have a 2000 Jeep TJ 4.0L incline 6 Sport.

So it's currently winter here in Canada and my Jeep wouldn't get up to temp. I decided it was time to investigate and on my day off I went ahead and took apart the housing for the thermostat. Low and behold, thermostat was broken. I had already bought another one and installed it plus the new gasket.

This is where I started to have issues. I don't so much work on my cat unless out of necessity since this is my first car. All I've done is basic maintenance and then I had to replace the transfer case (took me two days but it's been a year and it's still rocking ). So I thought this would be easy.

Anyways, I flushed out the radiator with some distilled water (only once because despite the heater it was cold working on the car) and then cycled some more distilled water through the engine and the heater core. I didn't do it until clean because I realized I misjudged how much water I had and ran out (and my outdoor hose is frozen so I was using distilled water and a hot water pump I have for camping.)

I emptied out the radiator and went to fill the system with coolant. It took about two of my 4L jugs before it wouldn't take anymore (including when I was running the engine to get it to pull the coolant down) so I filled the overflow reservoir, put on the radiator cap and went to take it for a drive. As I was driving my Jeep went up to temp, then kept climbing. I thought all I had to do was maybe add some more coolant but on my way back, the temp suddenly jumped up to just before the red and I turned it off. Coasted to the side of the road, waited a bit for the coolant to cool down. Added a bit more coolant and then rushed to drive it the 5 minutes home. I made it home and just as I was pulling into the garage it went just before the red again. So I turned it off. While I was stopped I also could feel the coolant bubbling like crazy in the rad.

I tried to burp out the air and all that. Anyways, here are my findings.

I've judged that the Water Pump is fine because I can feel the coolant being pumped through when I squeeze the upper radiator hose.

The thermostat seems fine because the upper radiator hose stays pretty cold until around 100 celsius (it's a 195 farenheit tstat) where it starts to warm up.

Fan works because it's mechanical and turns on when the car starts.

Now, eventually when running the Jeep the temp stays at around 110 celsius idle (which seems pretty warm for idle) and then after some revs it starts to climb.

When I was testing the engine after doing all this I let it warm up to 110, and then let it idle for about 15 minutes. Eventually I heard some boiling noises and when I checked, the coolant was boiling in the overflow tank.

I tried burping again. Car on an incline, radiator cap off, funnel in, engine on. The coolant would rise up the funnel and eventually start boiling. This confused me because I thought the coolant was supposed to go down as I burped it. When it got too much I turned the car off and let the fluid go back into the radiator. But as soon as the car was off I noticed that the upper radiator hose was completely empty.

I'm confused, I'm not sure what I did wrong and why it's not working. Any ideas or tips would be thankful before I take it to the shop tomorrow.

Thanks in advance.
 
Pull thermostat. Drill 1/8" hole in flange at the 12 o'clock position, put it back in. Run the engine up to temp with cap off of radiator, if it bubbles out lots of coolant right before thermostat opens, pull it and drill a 3/16" hole and put it back in clocked correctly. You have an air bubble issue we have noted in recent years that is solved by drilling the hole in the flange.
 
@mrblaine

Thank you! I will give that a try tomorrow. Crossing my fingers. Sorry for the repost as well, I've been searching all day and didn't come across that solution.
 
Pulling the temp sensor and filling the rad will allow a lot of air to escape the block. When the coolant starts to pour out, screw the sender back in. I would put a little fresh thread sealant on the sender first before you start adding coolant to be prepared.
 
@mrblaine The hole in the thermostat worked a treat. Got all the air out and on my short drive around the neighbourhood (I was in 4x4 cause we got a lot of deep snow) the temp didn't go over 100 celsius! Many thanks!
 
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@mrblaine The hole in the thermostat worked a treat. Got all the air out and on my short drive around the neighbourhood (I was in 4x4 cause we got a lot of deep snow) the temp didn't go over 100 celsius! Many thanks!
Mopar thermostats used to work perfectly at bleeding the air. Recent versions have the little jiggler changed to a design that no longer works as well and we get the big push of coolant up into the funnel right before it opens. Drilling the hole makes them work like the old ones.
 
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Yeah! That what I kept getting last night, the big push of coolant except it would start boiling. Air bubble was the culprit and I am beyond relieved. I can drive to work today! The minute I reinstalled the thermostat with the hole in it I could feel all the air being bled out as I filled the rad. I let it idle up to around operating Temp, it wouldn't go above 86 celsius (I have a bluetooth obd2 and Torque that helped monitor the temp). When I started driving I hit a high of 97 but as soon as I would be consistently moving (got out of my neighbourhood) the temp would drop a few degrees (assuming more airflow through the Rad).
 
Mopar thermostats used to work perfectly at bleeding the air. Recent versions have the little jiggler changed to a design that no longer works as well and we get the big push of coolant up into the funnel right before it opens. Drilling the hole makes them work like the old ones.
do you use that special funnel they recommend for the late model dodge hemi to burp the air?
 
It was just one that could be jammed into the top of the radiator and the liquid wouldn't leak out. I bought it at Canadian Tire (kinda like the Canadian AutoZone). It just fit well and worked. Then while it filled and ran I squeezed the upper rad hose a bunch and the air bubbles to the top of the funnel.
 
Hi everyone, I’m having similar trouble with my 99 tj. I have recently put in a new water pump, new fan clutch, new thermostat w housing. It started overheating very badly, into red, so I bought a duralast gold thermostat and put it in, it is still overheating but not as badly, not in red but over 210. Any suggestions? New rad?
 
Hi everyone, I’m having similar trouble with my 99 tj. I have recently put in a new water pump, new fan clutch, new thermostat w housing. It started overheating very badly, into red, so I bought a duralast gold thermostat and put it in, it is still overheating but not as badly, not in red but over 210. Any suggestions? New rad?
Is it blowing hot air out the vents?
NOT LUKE WARM...
HOT as in over 210 worth of hot
 
Not really, unless it’s well over 210. At around 200-220 it’s luke warm or even cool
Air in the system...
And or..
blockage at or going to the heater core..
And or..
Has anyone used that black shit in the cooling system to stop a leak?

I'd start looking into those things.

Is any of your heat issue RPM related? Just at idle...stop and go..Freeway speed...etc