2002 Dodge Stratus

My 2002 Dodge Stratus has approximately 90,000 miles on it. When it is warmed up and idling, the heater blows cold air no matter how high I set it. When I put the car in drive and start moving, the cold air coming out of the vents starts to warm up. The faster I go, the more heat I get. When I stop at a stop light, it starts blowing cold air again.
January 10, 2007.

One of three things: 1. Low coolant level. While you are checking the level, ask yourself. When was the last time you have the coolant system flushed? You may also have " air pockets" in the cooling system. Have you ever have to add fluid into the cooling system? If you or a service station used water, instead of coolant, that will reduce the quality and efficiency of the entire system.

2. Thermostat stuck open. Locate your radiator hoses. Grasp the hoses (one at a time) and squeeze them. Are they both warm to touch? If they are, the thermostat is possibly good. If one of them is warmer than the other, replace the thermostat.

3. Restricted heater core. This goes back to #1. If the cooling system has not been flushed for the past say 30K miles, you may have a lot of gunk in the system that prevents coolant flow, especially if you have been adding water or low quality coolant.

Follow the diagnostic from 1, 2, and then 3.

Please advise.

Jan 21, 2009.