Temperature Drops When Using Heater

[Mika H]

Hello I have a 1993 Corolla. The problem is that heater blows only cold air. I have changed thermostat and coolant. Temp gauge shows normal temperature , but when i turn on the heater to get some warm air into cabin all i get is cold air, and temp gauge starts dropping. If i continue using heater temp gauge goes all the way down to C letter. Can anyone help me with this?

[bigshark]

that is a wierd one!!

from previous experiences, our old car (rip) started blowing cold air through the heater and that was becuase the headgasket was gone!!

best to check your engine coolant to see if theres any white stuff in there!!

or another possible cuase would be that maybe air has got into the system.

[Mika H]

Thanks for the answer. I think that i have managed to solve the problem. I let the engine run without radiator cap, and then saw a few bubbles coming out of the coolant. Now I get warm air and temperature is normal. So the reason for the problem was probably air in the cooling system.