Well the story of the 92 Cherokee dad gave me continues on. Started it up today and with a laser thermometer checked the thermostat housing (and brass portion of CTS) and checked the rear CTS and the highest reading I got was 230, mostly hovered in the 210 to 220 readings. Electric fan not coming on but I can take care of that. The gauge itself is still pegged at over 260. Seems like it's staying there now. Possible bad ground? Are those the proper areas to check externally for coolant temps?

 

The infrared thermometers are not 100% accurate. I did a test with one. Infrared thermometer and a regular mechanical a/c thermometer (looks like meat thermometer) The infrared thermometer was reading about 10* cooler then the mechanical thermometer. Just sayin. Unplug the cooling temp sensor on the thermostat housing. See if your fan turns on. If it does then its telling you all the circuits are intact. from the pcm and the temp sensor.

 

That's a 30 degree or better error. Has the temp sensor ever been changed? The one for the gauge, that is?

 

Yes, both are new.

 

I agree with you. At the same time if you hold the IR thermometer very close to the unit being measured the accuracy is very close.

 

Anyone else?

 

From where?

 

Advance auto. Two of them doing the same thing.

 

mine has about 10 degrees difference, don't remember which way.