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Heat on blows hot while car is moving

I didn't notice this so much until recently because its just now start to get cold around here, but my heater only blow hot air while my car is moving. After I let the car warm up i turn up the fan, if the car is moving it will blow hot air into the cabin. As soon as I stop my car at a light or stop sign the fan still blows air at the same rate as before, but it is no longer hot. Soon after i start driving again the hot air kicks in. What could cause this type of problem. Thanks for the help guys!

It's possible you have an air bubble in your coolant system. How is your coolant level in the tank and engine temperature?

The engine temperature is normal but I will check the coolant level. Last time I looked (3 weeks ago) it was full, possibly slightly less than full.

I would take the time to inspect your cooling system just in case. I haven't had the X long or had to do much work on it so I don't know if there is any other likely culprit. I found this in an old post

Quote:

Originally Posted by Thermo (Post 458181)

... I do not follow any of the special bleeding instructions that have been talked about. There is a tube that runs off of the back of the engine that is at the high point in the block and it flows directly to the overflow bottle. Fill the system up with the engine off, start the engine and let it idle (with the cap removed). Add coolant as it gets low in the overflow bottle. Once level stabilizes, put the cap on and go for a short drive. If you feel it necessary, you can use the J-gate to force the tranny into a specific gear. That way you can force the motor to rev up to a higher RPM (say 4-5,000 RPM). This will help force the air bubbles that may still be trapped around to the overflow bottle. Park the car, let cool, then top off the overflow bottle to the "cool" line. You are good.

Crowlader, like was mentioned, it can be an air bubble in your coolant system causing this. Along those same lines, you may find that you have a water pump that is starting to go and what is happening is at low RPMs, there is too much leakage around the pump and it is not developing enough pressure to push the fluid through the heater core (hence why it is cooling down). But, you get the engine RPMs up, the pump starts working better and developing more pressure, there is now enough flow through the heater core to get things warm.

Along these same lines, if you have a blockage in the heater core, you can get the same sort of reduced flow through the heater core. I would be leaning more this way since you do not mention any overheating issues after slowing down from the highway. But, keep an eye on the temp gauge after a 20 or so minute drive on the highway and then stopping at a stoplight right afterwards. If you see the temp gauge climb a little bit, it is your water pump. If the temp gauge remains stationary, then odds are it is your heater core.

To clear the heater core, you will need to disconnect both heater core hoses and then using some compressed air (less than 80 psi), you will need to blow air through the heater core. This should dislodge anything that is stuck in there. You can use a small slug of water to "hammer" the blockage out. You will know if the heater core is good because you will find that air will flow very freely. ANy sort of blockage and you will see where the air flow will be hindered.