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Vernicious
November 10th, 2017, 13:58
I think my temp sensor is going south, but I wanted to see else it could be. I was driving home from work the other day and the temp outside was about 35*. I was sitting in traffic and my temp gauge went down to 2 ticks below 210. It usually sits about half way between 210 and the tick below it. The next day I drove to work and sat in a little bit of traffic. The temp was about 25* out and this time it came all the way down to the tick above 100*. I was thinking an air bubble could create this, but the last time I had one of those the temp went high, not low. I recently did a coolant flush and I don't believe that my system is working that well

Bent
November 10th, 2017, 14:47
I replaced the sender on my son's 96 and the gauge still reads hi. Either a bad sender or a wonky gauge. The temperature checks out at 210 +/- with an IR thermometer so for him (me) it's not worth the hassle to persue it further.

Tim_MN
November 10th, 2017, 15:04
Any helpful details about the vehicle in question ?

How old is the thermostat ? Is it sticking open ?

RCP Phx
November 10th, 2017, 17:21
Put a scanner on it! What year and motor do you have?

Wayne Sihler
November 10th, 2017, 20:41
Had this problem in my 98 recently.Random problem with the gauge dropping to 0,Some time in its previous life the wires from the O2 sensor were ripped off.
They were repaired,but a wire tie was used to pull the wires tight and pulled connection to the temp sender(sensor)loose.
I loosened the wires,un-pluged the connection,backed the sensor out,tightened it up and re-pluged the connector.
Cleared the fault and all is still well.

Vernicious
November 11th, 2017, 20:22
Any helpful details about the vehicle in question ?

How old is the thermostat ? Is it sticking open ?

My apologies, I meant to put specifics... It's a 99 XJ with the 4L and an AW4. Other than the lift it's all stock. The thermostat is a possibility. When I did the flush I planned on replacing the water pump, thermostat, fan clutch and rad cap. However, there was so much stuff left in the radiator and heater core I opted to just change the cap only. Over the winter I'm picking up a new radiator, heater core and hoses to swap out once the temp heats up a little. I have no idea how old the coolant system is in this vehicle. I've owned it for 2 years so I know the components are at least that old. I also have a trans cooler, and plan to replace the trans filter and fluid at the same time.

lazyxj
November 12th, 2017, 10:59
As suggested by RCP Phx, hook up an OBDII scanner and see what the digital temperature reading is.
Use an infrared thermometer to check the temperature of the thermostat housing, using the highest temperature detected as the 'right' temp.
If the thermostat housing reading is much different than the infrared reading, then sensor is probably bad.

I tried several sensors, on one of my Jeeps, before finding one that gave the correct temp, one that both the scanner and infrared thermometer agreed with.
Interestingly, a new Mopar sensor was off, a Delphi sensor was right on.

I suspect that with an old, un-serviced, cooling system, there is a good chance the thermostat is failing.
Changing a thermostat isn't a big job, you might want to do it now, if you are not planning on the cooling system rebuild in the near future.
It would also improved the heater's performance, nice when it's 25 outside.

Vernicious
November 12th, 2017, 18:08
Lazy, thanks for the info. I think you guys are onto something with the thermostat. Ironically when I noticed the real low temp it was about 28* out and my heater was blazing hot. That's what made me question what was really going on. I may just swap out the thermostat next weekend to see how it goes.

For the record my temp sensor is only holding on by the wires. I had planned on replacing it with the rest of the cooling system in the spring. If I have to do it now, I will.

ParadiseXJ
November 13th, 2017, 22:03
I think my temp sensor is going south, but I wanted to see else it could be.

What kind of shape is the sensor in?


For the record my temp sensor is only holding on by the wires..

Oh, nevermind. :doh: