After about thirty minutes of continuous run my coolant temperature gauge is closing in on the red line. The temp gauge says the engine is overheating. But the engine doesn't have any of the symptoms. I already replaced my thermostat and drained and refilled the system last week, and the truck wasn't overheating then.

I assume it's either a faulty coolant temperature sensor or a faulty coolant temperature gauge, but the possibility of overheating my engine and causing severe damage is too risky. How do I tell the difference between a faulty sensor and/or gauge and an actual overheating engine? If I just unplug the sensor I won't know anything, so I can't do that.

Please Help!!!

Vehicle Info:
1994 K1500 Silverado 4x4 5.7L TBI

 

professionals use a infrared temp gun.

 

Yeah, I actually work at a garage. The only issue was that this happened last night about midnight on my way home from work. No technician in sight, no tools, no assistance. I was hoping for a quick and easy test I could do to see if my truck is really overheating or if it's just a bad sensor or gauge. Driving it back to work (10 miles) is a risk if it's really overheating. So I was hoping for a more layman's method of determining the problem from home.

 

I don't know where you'd find one, but use a temp stick. Stick it on the engine, these things will melt or turn color at certain temps.

 

Try a mechanical gauge as a test.

 

Yea on the Mechanical Gage test like oldchevy said...

I have one of those older "Analog" Refrigerant Temp Gauges, the one with the dial indicator. I just remove the Rad Cap, slip the metal probe down into the fluid, and let the engine warm up real good. You may have to vacuum some of the Coolant down where it doesn't overflow. Just squirt it into the Reservoir, where the engine will pick it back up later.

What you should see is the temp of coolant that the thermostat thinks it needs to let by. That should be 195 if you have a recommended stat. Your gauge inside should read close to that, but, remember where the sensor is, SO, there may be a little difference there.

I guess it doesn't matter if it's off a little or a lot, as long as you know what's going on with it.

Remember to put your Cap back on when it's hot, then it will start the fluid recovery pretty quickly after you shut the engine down.

 

Well, I drained the coolant last night and inspected it to see if there was any oil leaking into it, or any sediment which could come from something plugging up the system. Found nothing but the sort or sediment one would expect from an engine that's this old.

Refilled he coolant and then drove it to work the next morning. It was fixing to overheat by the time I got there, but I was able to make it before the gauge read too high. Inspected everything again and no signs or symptoms of overheating. It's being repaired Monday by one of my technicians. I would have preferred to diagnose and fix it myself, but like I said, no tools here.

 

i would suspect a bad thermostat if it wasn't happening before you put it in....or air in the system