Temperature guage doesn't work and heat blows cold

Make sure that your radiator is filled to the proper level. If it isn't, the heater core may not be filled, so no heat can be extracted from it.

I believe the mazda protege has a separate thermoswitch to activate the radiator's fan. Perhaps the fan keeps blowing until the temperature is too low. Try replacing the fan thermoswitch. Just take care to put in tis place a thermoswitch of the same temperature range.

The problem is likely related to a failed air temperature control blend door, it is likely stuck or the electric actuator is defective which is most often caused by a sticking warped blend door in the air ducting. Yo replace these parts requires the entire dash be removed from the car, about a $1000.00 job.

I have a 2000 pontiac grand prix with a digital climate control system. The heat quit working, it doesn't blow out any heat. Now that it is warm outside the air stopped blowing out any air. The digital temperature on the climate control is not correct. When it states that it is below 30 degrees on the ext and it is warm outside the air wont be cold. Once it starts going above 30 degrees the air gets colder. Today the blower stop working all together. Was told it maybe the climate control unit was bad. You can hear the door opening/shutting when you switch the temp from cold to hot. But there was no heat blowing out whatsoever in the winter time. Could you please give me your opinion on whether or not it is the climate control unit or something else?

make sure you have plenty fluid in the radiator and the bottle. sounds like it is low.

So it works with a/c but doesn/t work with heat. Is that what your saying?
Or it blows cold air on heat selection?

If it blows but only blows cold air on heat selection
check out the following items:
temperature selector switch
blend door actuator and motor.



Here are a list of items to check out or have a shop inspect if it doesn't blow anything at all.
a) on/off switch
b) relay
c wiring
d) resistors
e) blower motor

Check to make sure it is full of coolant, if it is then the motor that controls the blend door is bad or stuck.

The HVAC controls could also be the problem.

unfortunately it sounds like a head gasket issue

Yes,it rules it out. The valve leading the water into the heater core is not opening or the door that put the air past or through the heater core is closed. This is general information not specific to your particular model.

I DON'T IT'S THE THERMOSTAT, BECAUSE I HAD THE SAME PROBLEM, COME TO FIND OUT IT WAS MY BYPASS HOSE BEHIND THE ENGINE THAT WAS LICKING THE COOLANT. CHECK COOLANT RESEVOIR.