started running hot while I was driving on the freeway?

1992 GMC SIERRA
300,376 MILES • 5.7L • V8 • 4WD • AUTOMATIC
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RODJAMES
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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?
Mar 12, 2024 at 8:00 PM
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STRAILER
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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 enlarge)
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Mar 13, 2024 at 9:47 AM
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RODJAMES
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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.
Mar 16, 2024 at 6:12 PM
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STRAILER
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Okay, that should help. let me know how it goes.
Mar 17, 2024 at 9:41 AM