Replaced water pump and thermostat, now overheating at idle

Alatex

TJ Enthusiast
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Followed the water pump replacement thread on here and the video it linked. Started the Jeep and it really seemed to run great. I also replaced the serpentine belt since I had everything off. I added some radiator fluid and was letting the Jeep get to operating temps and it just kept climbing. Once it got to the edge of the red line I shut it off and the fluid was boiling into he overflow and I had some light white smoke around the valve cover that I had never seen before.

Parts used were the parts listed in the thread. Fan is able to be turned currently with the vehicle warm. I have not driven it yet to know the temps when driving.
 
You've got air trapped in the system. Did you drill a vent hole in the thermostat?

From the forum:

20190617_080640-jpg.99797
 
Yes, most likely there's still air trapped in the cooling system. Drilling a hole into the thermostat's flange like shown below and positioning the hole at the top when installing it will help get rid of the trapped air more quickly. Some thermostats come with a vent hole already, just make sure to position it at the top when installing it.
Thermostat drilled hole.jpg
 
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Ok I definitely did not do that and missed it in the thread. Turns out I believe I was pretty low on radiator fluid and I’ve gotten the level back up and it seems to be hanging out around 210 now.

Do I need to go back in and drill the hole or will the air escape over time on its own?

ETA: Once I saw the fluid leaking and figured out it was the water pump, I parked it. That was about 3 weeks ago so I’m guessing more fluid leaked out than I had imagined.
 
you probably found your problem then. The hole isn’t mandatory, but it sure helps, and I did it.

But, if you saw that it was low, filled it, and it’s running correctly, you’re most likely good.


I would have at least flushed the whole system if you’re going to have it apart that way you know how much you put in.
 
There is an additional method of burping the air from your system:
https://www.amazon.com/gp/product/B01A2CQSU6/?tag=wranglerorg-20
Buy the above kit, install it into the radiator, instead of a cap. Add coolant into it. Run the engine, till it reaches ovprating temperature, and then you will see bubbles, if you have air.
This is in case your thermostat housing does not have bleeder screw, or the thermostat was not drilled for screw.
 
you probably found your problem then. The hole isn’t mandatory, but it sure helps, and I did it.

But, if you saw that it was low, filled it, and it’s running correctly, you’re most likely good.


I would have at least flushed the whole system if you’re going to have it apart that way you know how much you put in.

Only reason I didn’t is because I literally flushed it and put all new coolant about 6 weeks ago, so I was hoping it wouldn’t leak a ton just sitting and that I would just be able to replace what came out during the water pump install
 
There is an additional method of burping the air from your system:
https://www.amazon.com/gp/product/B01A2CQSU6/?tag=wranglerorg-20
Buy the above kit, install it into the radiator, instead of a cap. Add coolant into it. Run the engine, till it reaches ovprating temperature, and then you will see bubbles, if you have air.
This is in case your thermostat housing does not have bleeder screw, or the thermostat was not drilled for screw.

It was my understanding that the TJ will self burp over time
 
Over time maybe, but in this meantime you can get an overheat. This is why one needs to burn with this kit, or burp with using the bleeder valve, or use both. Using both might be the best option.
 
The level dropped because the air worked its way out. The hole isn't needed now, but this shows why it helps to do it up front.
 
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if you can run engine till it’s up to operating temperature without the radiator cap on the system will clear all the air by itself. been doing it this way for 40 years. it only takes a few minutes extra.
 
If it overheats again test your fan clutch, give it a spin by hand if it easily makes a revolution or several revolutions it is probably failing you can also do this test after it is up to temperature shut off the engine (obviously, lol) and give it a good spin again it should not spin easily.

mine the engine temp would fluctuate a little in just moderately warm days, then it started happening when using the air conditioning it was just on the warm side with random incidents of quickly rising temperatures. Towing my Aliner trailer up a grade it would run hot if the A/C was on at the same time it would quickly hit the red zone. Replaced my fan clutch with one off Amazon and it was perfect for about a week, then same thing. The cheep fan clutch off Amazon only lasted a week, so I replaced it with a less cheep one from Auto Zone and problem solved. Warning, the wrench to hold the fan clutch so you can unbolt it cost twice as much as the part you are replacing, you may be able to borrow the wrench you need from the auto parts store.