Here are the symptoms that just started yesterday, of course that was when it got cold outside.

I have a 2000 neon. It just turned over 100k miles. My temp gauge does not rise at all. The air from heater and defrost mode is luke warm at best. The car is not over heating, nor does it appear to be overflowing the overflow retention container. I just drove 100 miles and the air did not ever get warm. If it were the thermostat then wouldnt the car overheat?

The only thing I can think of is that the air blender door is not working correctly. Is there other things that could be possibly wrong that I can figure out with little mechanical knowledge?

 

Okay you had me a bit confused when you sais "my temp gauge does not rise at all", meaning My temp gauge does not rise at all above normal or it appears there is no function at all with the needle. I would lean against cloged heater core; if someone has used Bars Stop Leak it may have cloged the heater core. You may want to try reversing the hoses on the heater core and flush the system. then you will know for sure if the core had been cloged or not. another method to a cloged core that worked temporarly for me was to take a shop vac and hook it to the cores supply line and the return line in a 5 gallon bucket and run the bucket dry repeat process untill the water comes clean.

Keep us Posted

 

My daughters 2000 neon has been that way for years. thermostat replacement made no change ,the guage is barely in the operating rangeI took the last posts reply and went 1 step farther. Remove the heater hoses from the core. Take an old 5/8 garden hose ,cut it about 5' long on the swivel coupler side. Put it on the lower heater cor fitting and screw the other end to your hose sprayer, as long as its has the male threads. Now you can control the water flow. I went several times from the lower to upper and got junk out of it 4 times. No need for clamps unless its really clogged. thanks for the idea Garrette !

 

Hey, good news. I was confused for a bit because 2 days after posting this question, I had heat again and the temp gauge rose into the normal operating range. So I thought maybe the thermostat was just stuck. However, when it was working, it was also about 30-40 degrees warmer than the days in which it was not blowing warm air. Anyway, I bought the thermostat and since it started snowing yesterday, I decided to try the thermostat. I replaced. The old thermostat was in multiple pieces when I took of the bolts and housing, they all fell out.

This is a much better/cheaper solution that I was expecting.

Thanks for input