New Member
May 7, 2018
Roxborough Park, CO, USA
Hello, I'm having issues with my 2001 TJ overheating with coolant spraying out the radiator cap. I have replaced the Tstat, water pump and radiator with no luck. The heater blows hot then it doesn't so its a circulation issue. Unless one of my brand new parts is failing the only other thing I can find as a possible fix is the temp sensor on the tstat housing. If anyone has this issue or what could be the issue input would be greatly appreciated. ty
A lot of posts about this very issue if you care to scroll down the forum posts.

What parts did you use? Did you flush the cooling system with something like Thermocure?

Replace the cap or borrow/purchase a pressure tester?

With your 01, you need to check for a cracked head. Look down the oil fill cap and see if there's antifreeze bubbling up.

If you see "TUPY" cast in the head below the oil fill cap, it's already been replaced with the updated head.

You can get a combustion gas test kit at auto parts stores to test the cooling system to determine if the head or head gasket is compromised.
I didn't know that coolant could spray out of the cap, unless your cap isn't placed on properly, or if your radiator is blown. I had that problem once when my serpentine belt broke, and the lack of fan cooling blew my radiator. Check to see if you have sediment in the bottom of your coolant recovery bottle too, or if your coolant looks Jell-like. This has been a problem with PO's who didn't properly take care of their Wranglers.
Can you describe a little better what you mean about coolant spraying out of the cap?

If there is excess pressure in the cooling system my first suspect would be the head gasket.
Just to address your question, the temp sensor will not cause this issue - it is something else.

Your mention of the heater not blowing hot could be due to air instead of coolant in the system, especially if this happens after the coolant is blowing out the radiator Before this happens.
If you believe it's a circulation issue, have you flushed the system with Thermocure, and continued to flush it, until it's clear and clean, and free of residue particles? A clogged cooling system could be the issue if someone was mixing different coolants and messed up your cooling system. You should only use the recommended coolant specification easily verified by color and don't mix different coolant types. It has been known to cause casting sand and Jell-like substances in your cooling system which can clog it. See the pictures of another TJ cooling system with this sort of problem. Clearly, if you have stuff like this in your cooling system, it can clog it up. See the bottom of the collected flush in picture #2? You need to continue to flush your system until you see no residue particles. If it is caked, it may not all come out the first time, second or eighth time. It depends on how long it was left in that state. When it cools down, it cakes. Then, if the flow isn't great, it may not break up, and just continue to caked more and more. This issue has ruined some JK vehicles when the manufacturer changed coolant specifications, and just added the new coolant to the old coolant specification. Different coolant chemical compositions may be incompatible with each other and they may cause reactions, producing Jell-like substances and precipitations.

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