I'll be brief. 2002 WRX, 80k miles. Problem is that my heater is not blowing hot when the car is at idle, even after being fully warmed up. If the engine is at or above 2500 RPM, moving or not, the heater blows hot, like it should. If I then return to idle, the heater blows cold again.

The car is not overheating, not even running up to the second tick mark on the temp gauge.

Water pump?

 

I am thinking of a couple of things .

Thermostat that is stuck open and the engine cools way down when idling. Your temp gauge reading pretty much nixes this one.

You have a vacuum leak.

Fluid level in the cooling system is low enough that at idle there is now fluid flow through the heater core.

Just some thoughts.

 

+1 for stuck t-stat. check it out. ?

 

If t-stat stuck open, you won't even get heat when driving. It will actually get cooler and cooler. That what happened with my GSR. Like harvjens said, check your coolant level, temp and leaks. If your temp is cooler than normal, that your t-stat might be stuck open. If shouldn't be your water pump tho cuz you will be overheating if that's the problem.

 

well im not sure if is the same thing.

A/C doesnt work at idle also, you will have to drive it. if your car just sits at idle the A/C will start blowing hot air instead of cold, then start driving it or rev the engine, cold air will come out. nothing is wrong with it. it just that it needs power and gas. when your at idle, the a/c is not getting enough power to produce the heat or cold you need.

 

sorry to bump old threads. I was on my way home last night, everything was running just fine then i notice my temp gauge going up. It went up to hot. I was close to home so I got home and parked it for the night. I got up this morning and notice that it has leaked a lot over night. I let my car warm up this morning. It seemed to do just fine. As soon as I started to drive this morning I noticed it went all the way up to hot. I checked the overflow tank quickly and put a bit of water there but I am waiting for my car to cool a bit before I check the rest and add coolant/water to it if it is low. The heater works while driving but didn't seem to work as good at idle. The ac works while driving but i have not tested it at idle.

Any advice from anyone?