My heater just recently started to act weird. When I'm driving around, it blows pretty hot without any problems. But when I come to a stop, it gets really cold. It doesnt start getting warm again until I'm either driving or I rev the RPM's up. Anybody have any idea what be causing it? I hope the heater core isnt dying on me because I've heard they can be really expensive.

 

Either low coolant or you have air in your cooling system is my guess.

 

Air in the coolant, the voices tell me would cause overheating.



When the heater blows cold, check your temperature gauge. My guess is it may be showing engine temperature low (but even if not) I would put my penny on a bad (stuck open or cracked) thermostat. You could also have a partly clogged heater core. How does the coolant look?



also: tests you can do pretty easily: http://hubpages.com/hub/How-to-Deter...ostat-is-Stuck

 

Air in the system will not always cause overheating, especially if that air is trapped in the highest point (normally) in the cooling system...the heater core.



But you normally only get the air up there after draining and refilling the coolant



I would try flushing the system out, and flush the heater core by itself too, so you can see if it's flowing good.

 

Clogged heater core. Happened to a friend of mine. They werent able to unclog it so he had to buy a whole new unit. Wasnt cheap.

 

My wife's altima had air in the system with this problem. Had to park it on an upward angle and basically "burp" the car. Didn't know it was possible, but looked it up on a Nissan forum, and it did work.

 

Are you leaking any coolant? If you are, chances are your radiator could be shot. Does your temp gauge start to rise when idle as well as cold air being blown through the vents?

 

Mine is doing the same thing, I know I don't have air in the system because last yearwhen I changed the radiator I used vacuum refiller and put in fresh coolant. I was thinking either heater core or thermostat but my tempgauge stays where it always has.

 

If you're positive there's no air in the lines and your rad is in good condition, then it's either bad thermostat, bad heating core or low coolant.



Low coolant or bad thermostat are easy and cheap fixes. Bad core on the other hand....good luck.

 

as mad-machine once said



"the factory hyundai coolant gauge has 3 settings: cold, normal, and engine replacement"



dont trust it at all