Okay so from what I understand you don't have heat when your car idles, but you do when you're driving right?
Start by checking your level of coolant. With engine cold, your coolant in the radiator should be at least at the bottom of the radiator neck. In the overflow tank it should be a little over the cold mark. If it's low, add some GM 50/50 dex cool coolant (orange color), and check for leaks.
If your level of coolant is fine, check the following:
-when you first start the car in the morning (or whenever your engine is cold), grab the upper radiator hose with your hand; if you can feel coolant flowing through it, your thermostat is bad and you need to replace it. Also tell me: is your car taking an unusually long time to warm up? If so, try replacing the thermostat as well.
-with car idling at normal temperature and heat set on high, feel the heater hoses (the two smaller hoses that are hooked to the heater core inlet and outlet); are they both hot or is one of them much cooler than the other? If one is much cooler, your heater core is probably clogged up. Back flush your cooling system.
There are other possibilities for your problem but the ones above are the most likely. Come back if you need more help or if I misunderstood your problem.
Monday, November 10th, 2008 AT 9:36 AM