Started running hot while I was driving on the freeway?

RODJAMES

MEMBER
1992 GMC SIERRA
5.7L
V8
4WD
AUTOMATIC
300,376 MILES

My truck listed above K1500, started running hot while I was driving on the freeway. The gauge went well past the overheating mark then a couple minutes afterwards I noticed the gauge dropped down to the cold mark. Once I got off the exit and stopped at a stop sign the truck shuts off. I took the reservoir cap off for about 5-10 minutes to help cool down then waited probably another 20 minutes and went on about my business. The temperature gauge hasn’t worked since. What could be the issue?

3 Replies

KEN L

MASTER CERTIFIED MECHANIC
42,949 POSTS

It sounds like the engine coolant temperature sensor has gone out. But to be sure can I ask if the engine is full of coolant? If so, here is the location of the sensor so you can swap it out. This guide can help as well:

https://www.2carpros.com/articles/engine-overheating-or-running-hot

This guide can help walk you through the job with the location in the images below for your truck:

https://www.2carpros.com/articles/coolant-temperature-sensor-cts-replacement

Check out the images (below). Let us know how it goes.

Image (Click to make bigger)

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Wednesday, March 13th, 2024 AT 9:47 AM

RODJAMES

MEMBER
23 POSTS

The coolant was fine but then I noticed it was lower in the reservoir than usual and it didn’t go up to the hot fill line even after driving it. I also heard a hissing noise coming from the inlet radiator hose. So, I topped off the radiator then added water to the reservoir and now the coolant is staying at the same level in the reservoir. Also, I found that the coolant temperature switch which is number 7 on the image you provided was broken off. So, I am going to replace that one.

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Saturday, March 16th, 2024 AT 6:12 PM

KEN L