Ok. I have a gremlin ..lol. 90 model truck. Sr5 22re. In the mornings with the heat on and the vent switch set on the fresh air mode my temp hand starts to climb quickly above normal. The instant. And I mean almost instantly when I switch to recirculates or even the half and half position the hand falls to normal in the blink of an eye. Ive had Toyotas for 20 years and never had this happen before. Any idea what may be causing this. I guess I should include that I have the temp gauge that goes from C to H

 

Easy test for the gauge take the wire off it and touch it to a good ground with the key on and your gauge should go all the way to h when its grounded and back to c when you remove the ground.

 

Possibly an intermittent short to ground. Moving the recirc lever moves the wire? Check the wiring for continuity to ground either on the back of the gauge, or the sensor wire.

 

I'll try and test the gauge this eve. I had thought about throwing an after market gauge in anyway