I’ve noticed that my gauge is reading a pretty low operating temp. The image below shows the temperature after about 20 minutes of highway driving (and it’s even lower when actually driving). The corresponding temp of the t stat housing using an infrared gun was around 180.



I was curious what the temp of the t stat housing would read if I left it running until the electric fan came on. The electric fan turned on a bit after 210 on the gauge but the t stat housing was just shy of 240.




What could be causing this discrenpancy? One or both of the coolant temperature sensors? The t stat? Something else?

 

238 is pretty hot and indicates you are overheating. Maybe the metal can get hotter than the coolant? Is there anything else that indicates the engine is running too hot?

I had a problem where the coolant gauge on the dash showed too low because the coolant temperature sensor was bad. I'm not sure if it is the same for your jeep, but on my '92, there was a second coolant sensor near the back of the engine that fed info to the dash. I replaced it, and the problem was fixed.

 

It doesn’t seem to me that there are any other signs that it’s overheating. I have a 96 which also has a coolant temp sensor at the rear of the cylinder head like yours. That would make sense that this could be causing the gauge to read low but I don’t think it would explain why my coolant appears to be getting too hot. The other weird thing is that the electric fan is turning at the right temperature according to the gauge.

 

I believe there are two temperature sensors. One just for the gauge. And one that tells the computer the coolant temperature. Sounds like the sensor for the gauge is bad. Or the wire or maybe even a pocket of air in that area. And the other one is doing its job, telling the computer to turn on the fan.

 

I would make sure you have a 195 degree thermostat, bypass the heater diverter valve and remove, reverse flush your heater core separate from flushing your cooling system. If you still have overheating you may very well need a water pump as the impellers corrode and dissolve over the years reducing flow, The coolant temp sensor on the back of the head is for your dash gauge. If you have an OBD II reader, that will give you the temp from the sensor on the thermostat housing, which is what the PCM uses. Also depending the previous maintenance, you may also have a partially clogged radiator.

 

this^^^^^

 

If you have a scan tool you can see the temp the CTS is reporting, and check it against your infared tool to verify it's working.
I was experiencing low temps on the dash, and on my scan tool and infared which verified the temp was around 160 operating.
I have found (yesterday) that the T stat housing tends to build up huge amounts of scale right around the cts sensor. In the same venture I found my 195 Stant stat was sticking open. Put it in boiling water with my infared, it opened completely around 190 but then stayed open even completely cooled off. Not alot, but held up to light you can see light all round the edge. New stat and a good clean up and temps now up where they should be.=
I plan a complete flush and heater core flush.