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Discussion Starter #21
Hey, sorry to hear. Sounds like that's it. Just out of curiosity, how did you do the block test -- directly from the radiator I suppose? And did you ever see any other symptoms -- loss of coolant, lack of power, etc?
Yeah, tested right at the radiator neck. Aside from the mystery heating up issue, it runs perfectly. No white smoke, smooth idle, great power. The fact that is runs so well is the main reason I didn't question the test results when I did the early testing for a head gasket issue and everything showed the gaskets as fine.
 

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So I have an update....and it really sucks. I went ahead and replaced the coolant temp sensor, no change in the problem, then had a shop vacuum pull the coolant system to guarantee no air pockets, unfortunately no change there either. Feeling completely defeated I did the coolant block test one more time after the engine was nice and hot and the fluid changed from blue to yellow instantly, indicating exhaust in the cooling system...super bummed. Just for giggles I also bypassed the heater core again but this time I used clear tubing so i could watch the coolant flow. Above 2000 rpm the coolant is showing a bunch or small bubbles as well as several large air pockets in the tubing so i think it's safe to say that unfortunately I have a head gasket issue.

The worst part of all this is that I suspected a head gasket from the start because the price of the Jeep was so low, that's why I started with a compression test, cooling system pressure test and chemical block test, all came back fine. Apparently, my head gaskets are only leaking at high temps with the engine under load. I could have avoided weeks of work and hours spent replacing parts that were just fine if one of those tests had come back differently.

I also have a small leak at the rear main seal so I may just yank the engine and do head gaskets and other seals all at once.

Thank you all for the input on this issue, I really appreciate all the feedback.
I'm not say it is not the head gasket, it probably is but it might also be a leak in the oil cooler. I think there have been a few people with this problem.
 
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