J33P4L!FE

We just rebuilt the engine replaced everything under the hood. Well went to go break in the new cam and rebuilt engine today. Was running fin then noticed the temperature rose on it up to the red. The one radiator hose on the top was moving and you could hear the water/coolant bubbling. What would cause this to happen. It has new radiator, hoses, water pump, thermostat housing and a new thermostat. It is a 92 Jeep Cherokee 4.0L an has about 230,000 miles on it (before rebuilding engine).

BlueRidgeMark

Random ideas to toss around:

It's usually close to impossible to get the cooling system completely full without running it for a few minutes. You might just have been low on coolant.

Does it have a new radiator cap? Might not be holding the pressure properly.

It's always possible you didn't get the head torque right and your gasket is leaking combustion gasses into the coolant.

Did you get the thermostat in the correct direction? Did you test it before you installed it? What brand is it? There have been a lot of reports of bad-out-of-the-box thermostats with the cheaper brands.

J33P4L!FE

We think maybe a air pocket in it causing it to overheat. I put a factory thermostat back in it. And the radiator cap came with radiator when I bought the radiator kit. An for the head being torqued, we torqued it to spec with a $500 snap on torque bar my friend loaned me.

I was told to run it with the heat on also to try and keep from overheating.

BlueRidgeMark

You might have had an air pocket, but keep a close eye on it.

If you constantly have to run the heat to prevent overheating, something is very wrong.

J33P4L!FE

I appreciate the help and advise. I will let you know what happens when I go and try to fet it right this week.

J33P4L!FE

Went to try fixing the overheating problems today. Fired it up and let it idle for awhile and air bubbles were out of it. Went to to do break in and started to overheat. Relized that no fluid cerculating threw the upper hose into thermostat housing. Took hose off and poured cooant into hose till it would hold no more even after draing down. Hooked hose back up and let run without cap on again and then started overheating again. Not sure what the problem could be. Gonna get another thermostat and try that first but not sure what the problem could honestly be. Any ideas? Thanks!

T Shaw

Do you have a secondary fan? Does the fan come on when you turn your AC on? I had overheating problems with my 89 Cherokee and it turned out to be a combination of a bad secondary fan relay combined with a bad primary fan clutch.

BlueRidgeMark

I think you need to check for exhaust gasses in your coolant. This does not sound good.

J33P4L!FE

Didnt hook up second fan due to needing to finish ac lines and had to have one custom made so dont have top bracket that covers the top on and wouldnt think ot being cold outside and running at 2500rpm for 5min would cause to start overheating that quick. How would I check for exhaust gasses in the coolant?

BlueRidgeMark

Buy a kit.

https://duckduckgo.com/?q=test+kit+e...nt&ia=products

Easy to use, and then you will know.

67 GMC

I'd take the thermostat out and make sure you have proper flow in radiator and water pump hoses. You don't need it in warm weather anyway, it's designed to keep the water in the engine block until it's warmed up and then lets it go to the rad to cool down. If you remove it, you can eliminate the question of whether it's opening up at the right temp. Once you have everything sorted out, you can put it back in. For what it's worth, I've never had a "bad from the box" thermostat in my travels-they're pretty fool proof. I think people have other issues and assume it's a bad thermostat but I could be wrong.