Hi there,

So I have replaced the coolant temp sensor, the one on the back of the block several times. Its an '88 jeep cherokee, about 77k. I had one replaced from checker and the sensor was telling me that the car was overheating, it would almost go straight into the red after about 5-10 minutes of driving. I thought there was a serious heating issue, so I took it to this jeep speciality mechanic and they told me it was the temp sensor that I got and put on another one. About 50% of the time the gauge reads right with this sensor but then the other time it will read hotter in between 226 and 242 or what ever the two marks measure after 210. I have verified with IR gun that the car is not getting this hot, I took a reading at the sensor and it always reads about 205-210. About 185-195 at the thermostat housing. I am starting to wonder if there is an issue with the gauge, I am not familiar with the electronics of the gauge and I am thinking of taking it back to the mechanic or running to the junkyard and getting a stock sensor off an older jeep just to verify if it is the sensor. Is there another place to make sure I get a higher quality sensor?

 

could b wrong but when sensors go out most of time they leak fluid. but then again guages are natorious for going bad also.

 

Correct. You could be wrong. Temp senders on our Jeeps do not leak coolant when they fail.

 

There are two different temp SENDERS for our Jeeps. One for gauges and one for a warning light. Are you getting the correct one from the parts store?

 

Yeah its definitely the one for the gauge, the other one looks a lot different. Idk something else might be going on, I drove to work this morning and it was showing about 226ish on the gauge so I went and measured with the IR gun again and it was showing around 224 at the sensor and around 195-200 at the housing. I don't understand why it is getting that hot when it is only 60* out. It was about 80* when I took the reading yesterday and got about 195 at the thermostat and and 205ish at the sensor and I had been driving around for an hour before I took that reading, I only drove for about twenty minutes this morning. Back to the drawing board I guess...

 

How old is your thermostat?

I only use the factory stat # 83501426 anymore. Too many problems with aftermarket stats. Even well known brands.

Perhaps there is a restriction in flow near the sender? How's your coolant condition? Last time you flushed the system?

 

Thermostat was just replaced with that exact part number! It was flushed twice about three months ago, coolant appears to be fine, very clean.

 

Are your other gauges reading okay?

 

If it is hitting 220's the e fan should be coming on, is it?

 

No but where the sensor is on the radiator that is only getting to about 180-185*, sensor is on driver's side of radiator to the right of the electric fan as you are standing in front of the car. I think that fan is supposed to kick on when it gets to 218. I have no clue, I can say with confidence that it isn't really rising above 226* no matter what driving I'm doing. I just don't know what the hell its going to do when 90* + weather comes back, oh well might have to wait till next summer to diagnose lol. Sometimes temp gauge will sit around 200-210, and the other times it will do this. Its almost like there is air getting into the system everytime the car shuts off, thats the only way I can explain there are discrepancies everytime I drive. No leaks though so I don't know where this could be happening.

 

air pocket and/or crud at the back of the head? burp the system and make sure the level in your bottle is good maybe...dunno.

 

Do you have the standard cap on our coolant bottle or the Volvo cap?

Have you ever loosened the temp sender and allowed air to escape?

 

No I will do that, I was told that the best way to burp is to just let car run with cap off and heater switched to on, no fan running until it gets up to operating temp. At least that's what owner's manual says. And yes its that blueish cap, the volvo one. It ran fine coming to work this morning never got over 210.

 

You probably had a bubble then. cool. Pun intended.

 

lol yes very good! If you were to take the sensor off, I am assuming the rear of the car would have to be higher than the front to make air go to the back of the head there? Would you take the cap off of the pressure bottle, or leave it on?