Heater not working

I have an 01 Eclipse (55,000 miles) and the heater isnt working properly. I turn it on and it just blows cool air. It heats up when I am driving but when I am idle at a stop light it goes back to cool air. I have checked to make sure I have enough antifreeze, which I do. Does this sound like a thermostat problem or a heater core problem? If I take it to the shop how much do you think it will cost to get it fixed? Thanks for your help.

This thread should be placed in the 2000+ eclipse section.

How does the temp gauge look when your driving/idling. Does it get colder when you stop? If not then the thermostat is probably fine.

the temp guage stays the same. So do you think it is probably the heater core gone bad?

I really dont know man. Im not to familiar with that area. Im sure someone on here can help you out though.

Theres a couple simple things you can try to rule them out :

1 : Take out the thermostat , let the car idle - If the heater core is air locked , this will help release it.

2 : Adjust your inside / outside / hot / cold levers manually if possible to make sure they are opening and closing properly.

3 : Make sure your cooling system is full to manufacturers specs.

Thanks for the replies. I have tried moving the hot/cold buttons to see if anything was stuck but that didnt work. I also checked my antifreeze level and it was at the max line. I am not a car guy and so I would rather not try and take the thermostat off. I would rather not get ripped off at the car shop so can anybody tell me assuming the worst case what would be the most I would have to spend to get this fixed? Thanks again.

I also checked my antifreeze level and it was at the max line.

Just because you have plenty of fluid in the overflow tank doesn't mean the radiator is full too. Check that, and make sure it's topped off. I'm not familiar with the 3rd gens, but I believe the heater core is behind the passenger dash. Look on the passenger side floor mat and under the carpet to make sure the heater core isn't leaking. If none of that is evident, and you say all the linkages are hooked up for the temp control, then it might be time for a cooling system flush.