Instant Overheat
#1
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Location: Naples FL
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Year: 1999
Model: Cherokee
Engine: 4.0
Instant Overheat
Driving along and all is normal. Then it jumps up in temp to one notch below pegged and does it in less than 2 seconds. I shut off air, keep driving and in about 5 - 15 minutes it drops again from hot to normal in less than 2 seconds. Never get any steam or antifreeze smell. Any thoughts?
#2
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Year: 1996
Model: Cherokee
Engine: 4.0 HO Straight Six
Sounds like your gauge my be giving you an incorrect reading...
In reality, I don't think your coolant is going to change that drastically so quickly.
Verify your temperature with an infrared temp gun.
In reality, I don't think your coolant is going to change that drastically so quickly.
Verify your temperature with an infrared temp gun.
#5
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Model: Cherokee
Bad temp sensor. The PCM in those years drives the gauges and it can exaggerate the gauge reading by driving it nearly full-right when it thinks you are overheating....to get your attention.
#6
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Year: 1999
Model: Cherokee
Engine: 4.0
I changed the thermostat and temp sensor and it still acts up. Today I figured out the a\c doesn't have anything to do with it. It ran along at the normal temp (1 line past 210) then jump up to the first red line in about 2 seconds again. I just kept driving and it eventually dropped back down all of a sudden. I checked the top hose temp when it said it was over heating and it was 219. I check the wires for continuity to the PCM and they were good. The book seems to show only 2 outputs from PCM to the whole instrument cluster so I don't know what to make of that. Also don't understand why there is a return wire to the sensor. I figure its either got to be a bad wire from PCM to gauge or the PCM itself which I can't afford, especially if I'm not sure it the problem. What happens if the PCM doesn't get temp info? Can I replace with different gauge. Any tests I can do to see if it is PCM?
#7
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Year: 1998
Model: Cherokee
Engine: 4L
Very well could have air trapped in the cooling system. Park with the front end up hill and pull the cap off the radiator (while the engine is cool) then wait for the T stat to open and check or fill your fluid while holding the throttle partly open. Good luck.
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#8
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Year: 98
Model: Cherokee
Engine: 4.0
^^^^ this x2. I just did mine this morning an make a habit of burping the radiator once every six months or so for good measure. What happens is the air pockets let the water evaporate an turn to steam. When it goes past the temp sensor it will cause it to jump high an then when u start pushing water past again it drops to a normal reading. This should fix your problem.
#11
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Year: 1999
Model: Cherokee
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I checked for air, didn't seem to be any and it's still doing it. My brother says he had to pull the hose off and fill his system on his older cummins truck to get the air out. I talked to a computer repair place and they said "maybe, bring it in and we'll check it" I guess it's my next step if I can't find something else. Does anyone know if those computer diagnostic plug in things read water temp. I would like to be able to read what the sending unit is saying verses what the computer says it's saying.
#13
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Year: 1998
Model: Cherokee
Engine: 4L
Originally Posted by markcrain
I checked for air, didn't seem to be any and it's still doing it. My brother says he had to pull the hose off and fill his system on his older cummins truck to get the air out. I talked to a computer repair place and they said "maybe, bring it in and we'll check it" I guess it's my next step if I can't find something else. Does anyone know if those computer diagnostic plug in things read water temp. I would like to be able to read what the sending unit is saying verses what the computer says it's saying.
#14
My jeep overheated after driving 1 block... I had,a clog in the radiator from corrosion from the old owner who never ever put antifreeze in... -.- anyway it blew a small hole si thus, instant overheat
#15
Originally Posted by markcrain
I changed the thermostat and temp sensor and it still acts up. Today I figured out the a\c doesn't have anything to do with it. It ran along at the normal temp (1 line past 210) then jump up to the first red line in about 2 seconds again. I just kept driving and it eventually dropped back down all of a sudden. I checked the top hose temp when it said it was over heating and it was 219. I check the wires for continuity to the PCM and they were good. The book seems to show only 2 outputs from PCM to the whole instrument cluster so I don't know what to make of that. Also don't understand why there is a return wire to the sensor. I figure its either got to be a bad wire from PCM to gauge or the PCM itself which I can't afford, especially if I'm not sure it the problem. What happens if the PCM doesn't get temp info? Can I replace with different gauge. Any tests I can do to see if it is PCM?