Defiance, thanks much for that....it is VERY useful information. I copied it to my Jeep file.

 

Back to running too cool......does the heater work good? If so, the gauge reading is probably whacked.

 

Back to the OP, since you are taking the guage's word for how hot you are running, your Temperature Switch may be faulty. This sensor sits at the front of the head, which sends a signal back to the guage and gives you a temperature reading (this also depends on the year of your rig. From my understanding, any XJ 91+ has this sensor in addition to the Coolant Temperature Sensor that sits in the radiator). My guage does the same, reads at about the 1/4 mark, and i know that is not the correct temperature since my cooling system is all old and every component needs to be replaced. I just ordered this sensor from Autozone for 15.99 and it should be coming in the next day or two and I'm hoping this will fix my problem.

 

I believe on '96 down, the dash gauge gets it signal from a temp sending unit located in the back of the head/drivers side. The ECU gets it's signal from the coolant temp sensor located in the t-stat housing at the front of the head. '97 up there's no sending unit in the back of the head....the dash temp gauge gets it's signal solely from the ECU based upon info received from the coolant temp sensor in the t-stat housing at the front of the head. Believe XJs with the sensor in the radiator were '90 down or Renix XJs.

 

I dealt with this problem for more then a year and ive just fixed tonite i used 4 autobarn thermostats and thats when it started happening taking for ever to warm up i bought a duralast thermostat 195 and now its warm as it should

 

Hold on to at least 1 autobarn, may need it next summer. LOL