The temperature goes up we have to turn the heat up to cool it down?

JEEPERJEEPING

MEMBER
1999 JEEP CHEROKEE
231,534 MILES

I have a jeep grand cherokee and it has 231,534 miles on it and it runs pretty good. We have one small problem we start the truck, start driving and wait for the truck to warm up and wen it finally does the temperature goes up we have to turn the heat up to cool it down and then it runs fine no problem. Well everyone in awhile when it rans the engine will smoke for about 5 seconds and then it stops and doesn't do it again until the next it rains. Last night I was at a light and the temp started going up and some smoke came out of the engine and I turned the heat and it didn't do it again. I would like to know what the problem is because like I said it runs real good but just that one problem.

1 Reply

SQM

MECHANIC
6,383 POSTS

Hello,

This issue could be due to the cooling fan not coming on. Which could be due to a faulty coolant temperature sensor.
When the heater gets turned on it will make the cooling fan run, this cools down the engine. But when the heater is off the fan shuts down and does not turn on due to not getting the signal from the temperature sensor.
The sensor changes its resistance with the coolant temperature, which is the signal the ECM uses to determine the temperature of the engine, a malfunctioning sensor can send the signal that the engine is 'cool' to the ECM and that keeps the fan from turning on.

The coolant temperature sensor is installed in the thermostat housing (see diagram below).

https://www.2carpros.com/articles/how-a-coolant-temperature-sensor-works
https://www.2carpros.com/articles/symptoms-of-a-bad-coolant-temperature-sensor
https://www.2carpros.com/articles/coolant-temperature-sensor-cts-replacement

I have attached diagrams for your reference.

Please let me know if you have any questions.
Thank you.

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