[JoeTheHoboAanenson]

Hello all, my name is Joe, and i am currently the owner of a 2000 Jeep Cherokee Classic. It is 4wd, 4 door, 4.0 straight six. I had to replace the freeze plug on the back of the head, and ever since i had to do that, it has been nothing but problems. it has overheated alot. got a new radiator, new thermostat, new temperature control sensor and new water pump. still tends run a bit over 210 degrees. the hottest that it got was to the first white line after 210 degrees. im not sure how hot that is. but just recently, it just died. Just plain quit running, im a die hard jeep fan, but am wondering what the crap is going on here. any help would be greatly appreciated!

 

[Dave Z]

Keeping in mind I have NO 4.0 experience, but it sounds like the old 2.2 / 2.5 used to be when there were a lot of air bubbles in the system. It sounds as though there's an internal blockage of some kind. I also have to ask, is your fan functional?

 

[MoparNorm]

Was the old "freeze plug" (casting core plug) removed or knocked into the head?
Plugs knocked into the head can clog or block the water flow.
There may also be rust or corrosion in the water passages that needs to be flushed out of the system.

 

[ImperialCrown]

The causes for overheating can be diagnosed fairly easily (in most cases) by following the troubleshooting methods outlined in most 'competent' service manuals.
Any debris left in the system from a past service or accumulated over time from bad or old coolant/hard water will wash into and restrict the narrow passages in the radiator and heater core. Some radiators are beyond flushing when the internal blockage build-up is immovable. This can greatly reduce cooling performance if everything else is in order.

 

[Dave Z]

Hadn't even thought about the freeze plug being knocked IN. That's a good thought.

 

[MoparNorm]

The causes for overheating can be diagnosed fairly easily (in most cases) by following the troubleshooting methods outlined in most 'competent' service manuals.
Any debris left in the system from a past service or accumulated over time from bad or old coolant/hard water will wash into and restrict the narrow passages in the radiator and heater core. Some radiators are beyond flushing when the internal blockage build-up is immovable. This can greatly reduce cooling performance if everything else is in order.

I was tardy in checking back, my comments regarding flushing, were incomplete, I was referring primarily to flushing the block.
When i rebuild motors, you cannot believe the amount of crud I find in there, up to and including core plugs and casting rod pieces, along with an occasional 4 lbs of rust.

 

[TWX]

Moving to Tech Support...

 

[JoeTheHoboAanenson]

Keeping in mind I have NO 4.0 experience, but it sounds like the old 2.2 / 2.5 used to be when there were a lot of air bubbles in the system. It sounds as though there's an internal blockage of some kind. I also have to ask, is your fan functional?

Yes the fan is functional.

Was the old "freeze plug" (casting core plug) removed or knocked into the head?
Plugs knocked into the head can clog or block the water flow.
There may also be rust or corrosion in the water passages that needs to be flushed out of the system.

That was replaced, i had to do that because it was corroded, had a little hole in it. THat was a common problem with the 4.0's

I was tardy in checking back, my comments regarding flushing, were incomplete, I was referring primarily to flushing the block.
When i rebuild motors, you cannot believe the amount of crud I find in there, up to and including core plugs and casting rod pieces, along with an occasional 4 lbs of rust.

HOLY CRAP!! 4 lbs???

Hello all, my name is Joe, and i am currently the owner of a 2000 Jeep Cherokee Classic. It is 4wd, 4 door, 4.0 straight six. I had to replace the freeze plug on the back of the head, and ever since i had to do that, it has been nothing but problems. it has overheated alot. got a new radiator, new thermostat, new temperature control sensor and new water pump. still tends run a bit over 210 degrees. the hottest that it got was to the first white line after 210 degrees. im not sure how hot that is. but just recently, it just died. Just plain quit running, im a die hard jeep fan, but am wondering what the crap is going on here. any help would be greatly appreciated!

Turns out it was a cracked head, so 1500 bucks later (i dont have enough time to get it done myself) it seems to be running fine! Praying to God, that it stays this way for another 150,000+ miles.