help! heater cold when idleing, hot when driving

The heater in my wife's 90 lumina apv blows cold air when sitting still, but once you start moving the hot air starts blowing. I have checked the water level, bled the air from the cooling system still the same. Could it be my water pump going out? any other ideas would be of great help. Thanks

The symptoms you describe sound very typical of low coolant or an air pocket in the coolant system. Some of the Lumina motors are difficult to bleed and there are additional special bleeder valves located on the engine for just this purpose. Check to see if you have one on top the thermostat housing- where the upper radiator hose meets the engine. Consult your car repair manual on the specific locations.

I think if you had water pump problems, then your car would also probably be having overheating issues. Are you going through coolant- even if just a little each day??


Another possiblity is the hot/cold door in the ventilation system. Could be switching to full cold at an idle, but this seems less likely. Maybe you can get down there and listen for it moving while the wife drives.

Do u have a engine temp gauge, and does it move also, or just an idiot light.

Sound like you have a thermostat stuck in open mode. Amongst other possibles, there may be a vacuum hose or two either leaking; or misrouted. My bet lays on the former. Some thermos have a "open in failsafe" mode that prevents damage to the engine from hi-temps upon thermo failure. It would help to recheck all vacuum hoses related to airbox controls; as linear cracks are hard to spot.

the temp guage shows proper temps. I noticed one drop of coolant on the bottom of the lower hose when i changed the oil a few weeks ago. i bled the system through the bleeder on the thermo housing, no help. I know of the bleeder on the thermostat, are there any more?