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redundant heater question

F

fixerupper

Well-known Member
My son's 93 Cutlas Supreme that he just bought yesterday has real good heat out of the heater while sitting still but goes ice cold while driving.

This very same problem was posted by someone else a few days ago but I can't find it now. Seems like someone had mentioned the water pump impeller.

He can hear the air sounds changing under the dash when he moves the dash controls from one function to the other so some doors are moving under there but how well and which ones is unknown. Any quick ideas? First thing that comes to my mind is loose water pump impeller. I told him to try sitting there in park and revving the engine for awhile. That'll eliminate a stuck open vent door. The previous owner, who is a close friend said the heater worked fine the last time he drove it a couple of weeks ago. Thanks, Jim
 
Stat is stuck open. At low speeds the electric cooling fan will regulate engine temp. On the highway there is enough airflow to overcool the engine.
 
maybe the vaccuum switch for the controls. You have more vacuum at an idle than at driving speed. try running it at 2500 rpm while sitting and see what happens. Or the t stat like was said earlier
 
I agree with B&D...for another reason. I had a '92 Tempo that had a bad electric cooling fan. The car never overheated on the highway, because the airflow through the radiator adequately cooled the engine. But you didn't dare sit in a McDonald's drive-thru, unless you were the ONLY car in line.

So his point about cooling the engine with moving air is more than valid. And, as he pointed out, the electric cooling fan is adequate to regulate engine temp at an idle. I'd guess the stat is stuck, but not stuck completely closed.

And what year did GM switch from vacuum controls to electrical/electronic servo motors on the temp and blend doors?
 
I got a little forgetful when I posted. Replacing the thermostat was the first thing he did. Sorry I didn't mention it, however, the new one could be defective? He mentioned the air goes cold, not just cool. I'll relay the low vacuum suggestion to him. It has a four cylinder.Jim
 
Now he tells me it's the 3100 engine but the head gaskets have been replaced. I'm about to give up for the night and sit down in front of the tube with a brew in hand.

The cruise doesn't work, which could be several things, but the servo works on vacuum. He only paid $300 for it and it's just a bang around car so he's not whining about this, but a little heat in the cabin this time of year helps lift the attitude a bit. Jim
 
GM has never used vacuum controls on a blend air door. On a 93, it is a cable from the control to the door. Sounds like there is an air bubble/low coolant level.
 
Does it have the manual or auto temp control? Either way,there is no cable to the temp blend door.Both adjusted with actuator motors on the '93.

If it has the auto temp option,you can enter diagnostic mode by pressing "outside temp" and "bi-level" buttons at the same time and any codes stored will be displayed.If no codes,"00" will display.

Could be coolant flow problem too,but might as well start somewhere.
 
Brian, I think you're right. He parked it, walked away for an hour, came back and drove it and had plenty of heat. Couldn't even hold his hand by the vent for long cause it was so hot. Must have been a bubble. All this for nothing! (sigh) Jim
 
I had that problem. I put a GM thermostat in even though the Motorad was new. I think I also had an air pocket. The heater is much better with the OEM thermostat. Dave
 
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