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Discussion Starter · #1 ·
first off ive got a 95 yj 4.0l 5spd w/ about 130k miles on it.

So, recently my jeep has been running at a very low temperature (120deg.)

On saturday morning, after a really cold night in ct i had a really hard time starting my jeep. Once i got it running the temp immediatly started climbing and ended up boiling over in a matter of 10 minutes.

I shut it off right then and let it sit for a little bit and then re filled the anti freeze and was on my way.

I instantly noticed that the jeep was running colder (about 120-130). I drove it on the highway for an hour and went on a trail ride for 5 hours saturday afternoon and the temp never went above 130 degrees.

when i got home saturday i replaced the thermostat ( which was open when i took it out) but im having the same exact problem wth the new one. I covered the radiator with cardboard and left it running for an hour and then drove around for half an hour and the temperature guage didnt move past 130 degrees.

I took the radiaor cap off to see if there was circulation and even with the throttle pinned there was almost none.

The heat is warm but not hot and im getting pretty poor gas mileage.

ive been looking around all the forums but havent had much luck so any and all ideas are welcome.
 

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Nothing dripping from the water pump area? Any noises from the water pump? That's what come to mind anyway.
 

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Thermostat would have been my first guess too. What are the chances that the new one is faulty as well? You may want to replace your radiator cap or have it tested. System might need a good cleaning out? Sorry, out of ideas. Good luck
 

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Discussion Starter · #4 ·
Nothing dripping from the water pump area? Any noises from the water pump? That's what come to mind anyway.
nope.. everything is dry and there is no weird noises...

Thermostat would have been my first guess too. What are the chances that the new one is faulty as well? You may want to replace your radiator cap or have it tested. System might need a good cleaning out? Sorry, out of ideas. Good luck
thermostat seems like the obvious thing.. but it can really only be broken in 2 ways; stuck open or closed. if it was stuck open i would be getting lots of circulation through the radiator at all times.

if it was stuck closed it would overheat like it did the first time.



one thing i should probably mention is that it gets up to the 120 degree mark in the same aount of time it always took, now it just stays there.

I also noticed that the thermostat does move up and down a little as if the thermostat was opening and closing but its way below the 195deg "switch"
 

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How cold is it there? What's your normal operating temp? Maybe water pump. It doesn't really make since to me though. Also what are you getting your temp readings from maybe it's wrong try double checking temp with a temp gun
 

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Take the radiator cap off, make sure the fluid level is up almost to overfull in the radiator, and start it up. Let it sit there and idle up, watch the fluid in the radiator. If the thermostat is working, once it reaches temp you'll see the water moving in the radiator as it circulates. If it doesn't move...time to check the pump and/or hoses...if the hoses are old and really flexible, it DOES happen that the suction of the water pump 'closes' one hose down just like squeezing it! Hoses should be FIRM and not squeeze down easy under your hand grip. Also, before you fill the radiator up when you take the cap off...look for gunk in there...if it's full of gunk the radiator may be clogged and not allowing water through...which would make it overheat...not the problem you are having...hummmmmm....not much to work with here! Radiator, water pump, thermostat, and hoses...that's about it!
 

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I agree there isn't much left.I would think you got an old 150deg or a bad thermostat. Put it in a pan and boil it to see if it opens.(wait till the wifde goes to the mall)
 

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..................(wait till the wifde goes to the mall)
lol.....yeah, I got the same problem.

I got nothing more to add to what anyone else has said here. Its not a complicated system unless you have altered it with a heat exchanger or some other device. In which case.....:bottom:
 

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What did the gage read when it boiled over. Maybe the gage is bad and gets stuck at that point. I don't trust any of my gages,none of mine read rite. Just a thought.
 

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Discussion Starter · #11 ·
How cold is it there? What's your normal operating temp? Maybe water pump. It doesn't really make since to me though. Also what are you getting your temp readings from maybe it's wrong try double checking temp with a temp gun
its been pretty cold here but today it was almost 40 and i let it run for half an hour and it was the same way.

the jeep used to run right at about 200.

havent checked it with a temp gun but i can stick my finger into the antifreeze after its been running for an hour.

Take the radiator cap off, make sure the fluid level is up almost to overfull in the radiator, and start it up. Let it sit there and idle up, watch the fluid in the radiator. If the thermostat is working, once it reaches temp you'll see the water moving in the radiator as it circulates. If it doesn't move...time to check the pump and/or hoses...if the hoses are old and really flexible, it DOES happen that the suction of the water pump 'closes' one hose down just like squeezing it! Hoses should be FIRM and not squeeze down easy under your hand grip. Also, before you fill the radiator up when you take the cap off...look for gunk in there...if it's full of gunk the radiator may be clogged and not allowing water through...which would make it overheat...not the problem you are having...hummmmmm....not much to work with here! Radiator, water pump, thermostat, and hoses...that's about it!
like i said before.. it never gets up to temperature so there really is no circulation.

If water wasnt getting through then ude thing the car would overheat

lol.....yeah, I got the same problem.

I got nothing more to add to what anyone else has said here. Its not a complicated system unless you have altered it with a heat exchanger or some other device. In which case.....:bottom:
havent done nething with the system

Clogged heater core?
nope.. i get warm air

What did the gage read when it boiled over. Maybe the gage is bad and gets stuck at that point. I don't trust any of my gages,none of mine read rite. Just a thought.
Just got right into the red and then i shut it off. The guage moves around but just never gets to where it should be and my heat never really gets hot.
 

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Clutch on rad. fan locked up (does it freewheel)?
Did you burp the system when you filled it (air pocket)?
Try another thermostat. You may have just got a bad one.
 

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Discussion Starter · #13 ·
Okay, so heres how this story ends. After flushing the cooling system, replacing the top hose and thermostat, the problem persisted. I knew that the problem had to be related to either the temp guage or thermostat. I tested the tem guage and it worked fine, si I reluctantly pulled the new thermostat and damn if it wasnt stuck open!! I replaced it with the most expensive one they had at the parts store and within 5 minutes I was up to temp and everything is running fine since.

Thanks for all the feedback. I guess just cause its new doesnt mean it aint broke.

3 thermostats and 5 hours of work to fix, but my 4.0 is super clean inside now
 

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Okay, so heres how this story ends. After flushing the cooling system, replacing the top hose and thermostat, the problem persisted. I knew that the problem had to be related to either the temp guage or thermostat. I tested the tem guage and it worked fine, si I reluctantly pulled the new thermostat and damn if it wasnt stuck open!! I replaced it with the most expensive one they had at the parts store and within 5 minutes I was up to temp and everything is running fine since.

Thanks for all the feedback. I guess just cause its new doesnt mean it aint broke.

3 thermostats and 5 hours of work to fix, but my 4.0 is super clean inside now
You know thats interesting and thanks for the follow up. Its about the 4 guy who has had that problem with a brand new Thermostate. Hmmmm.....
 
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