My temp gauge reads all the way cold even though my heat is blowing hot. Sometimes it reads normal operating temp while I'm driving and if i turn the heat on it drops all the way back down to cold. Suggestions????

 

Car? Engine?

Replace the thermostat and bleed the cooling system. Then go from there.

 

91 EF sedan w/ Mini Me. Thanks for the tip. I thought it might be thermostat i just wanted another opinion.

 

Probably a loose connection/break in the wire between the gauge and the sensor. The temp sensor is a 1 wire sensor on the left/passenger side of the head directly under the distributor.

 

Definitely check that the sensor is connected properly. The clips that hold the wire on become brittle over time due to heat.

 

Thanks F22MASTER. That makes sense because the heat works perfect, its just the gauge that has a mind of its own.

 

This^ makes me think the gauge and sending unit are not the cause and that it's a cooling system problem.

 

If the heater is blowing hot, then the temp gauge should be at least 1/4 of the way up the scale.

If the heater is blowing hot, and the temp gauge is below that, you have a guage/sensor/wiring problem.

 

Not necessarily. For example, air trapped in the cooling system could cause the temp gauge reading not to correspond to the actual coolant temperature, and also cause the reading to register correctly only intermittently.