The heat in my 91 LX was working although not that strong up until about a week ago and now I get nothing at all. Granted, its about 7 degrees here but its actually colder to have the heat on in my car right now b/c it blows very cold air. Is this definatly a heater core problem or could it be something else I can check?

 

I just had this problem with my '90 GT, I changed my thermostat.... got a 180 degree one although I probably should have got a 195, my heat still doesn't get hot....just warm. In my thread I started people told me i'd know it was the heater core if I could smell antifreeze inside and the car and it was leaking on the passenger side floor. Other than that I don't know what to tell you,

 

A higher temp thermostat might fix the problem. The other issue is, if someone put bars-leak or other type of radiator sealer, this may have clogged the heater core. While replacement is the best option, a temp fix that *might* work is removing the hoses that go to the heater core, attaching two new hoses, and leaving them unconnected, pouring Draino or Liquid Plumber in them for 15-30 min. Then use a hose to blow it out in BOTH directions, and then reconnecting the heater core hoses.

Hopefully one of these works. Good luck.

 

I just replaced my water pump today and the air coming out of the vents is definitely hotter. I suspect something was blocking circulation in the pump, so that may be another thing you want to check.