I have a 97 Honda CRV that I just had Timing belt, water pump and other belts replaced on. What I am noticing now is that the car runs fine but if I put the heater on the car shows it is overheating. I can turn off the car and start it again and the temperature is back to normal. As soon as I put the heater on the temperature gauge starts climbing again. Anyone know what might have gone wrong?

See if this link helps:

https://www.askmehelpdesk.com/cars-trucks/faq-how-troubleshoot-repair-maintain-hondas-selected-other-vehicles-46563-11.html#post2043857

Since engine temperature normally drops when the heater is turned on (it acts as another radiator), the thermistor in the ECT Gauge Sending Unit may be bad. Resistance should increase with the decreasing temperature, when the heater is turned on; however, it's not acting now as a NTC thermistor.

Hi TxGreaseMonkey,

Thank you for your reply. Do you know where ECT is located on 97 CRV? Would the outside temprature sensor have any roll in this also?

The ECT Gauge Sending Unit is likely located under the distributor. It has a one-wire connector going to it--this is the one you are interested in. The ECT Sensor, which goes to the ECM, has a two-wire connector going to it--ignore this item. Both of these components are usually located next to each other. Drain the radiator to a level below the sending unit, prior to removal.

The outside temperature sensor should have no bearing on the situation.

Thank you. I will try this out over the weekend and put a response. Appreciate your time and help.