1988 - Poor Heat in Cold Weather - Need Suggestions

In colder weather, the heat output is now so poor that this vehicle is not at all comfortable to drive. Last fall I replaced the heater core due to a leak. I thought perhaps I messed up the damper door that controls air flow through the heater core. But, I have checked it and it is in the right position when it is cold. There is lots of air flow, but the air temperature even when the engine is warmed up is just barely warm. I replaced the engine thermostat, and that changed nothing.

About all I can conclude is that I am not getting enough coolant flow through the heater core. Any suggestions on what could be restricting the flow? I presume there is no flow control device in the coolant circuit? Could it be that the water pump is not putting out enough flow? There is no indication of engine overheating.

All suggestions appreciated,

Ron

I would replace the thermostat and both gaskets. This is a common issue and is quite often fixed with just the thermostat.

Any thoughts on how old your current one is?

I would replace the thermostat and both gaskets. This is a common issue and is quite often fixed with just the thermostat.

Any thoughts on how old your current one is?
I just replaced the thermostat with a 195 F and it made no difference. GM uses a totally stupid system to hold it in -- with a single bolt on one side. I played around with it for about an hour and put a shim under the bolt to get the cover to sit square and hold the thermostat down so it would not bypass. The o-ring was replaced as well. Are you saying there should be a gasket under the thermostat? If so I did not replace that.

Ron

There are two gaskets on the housing. One sits in a groove around the outside of the housing. The other sits in the inside diameter of the housing and will sit flush with the thermostat itself.

9 times out of 10 the housing won't sit parallel to the mating surface of the engine so don't worry about it if it wont. As long as the bolt is fairly tight and it doesn't leak then its fine. Later versions had 2 bolts after designers apparently figured out that just the one kinda sucks.

There isn't any other sort of coolant flow control other than the water pump. When was the last time that the coolant was flushed? It should be done every couple of years to avoid build ups of deposits.

I doubt the WP is the culprit but you can always remove the belt and spin it by hand. As long as it doesn't wobble, squeak, grind, or leak then it should be fine.

How is the air output? Does the blower motor kick on and at least push out air? Can you hear it engage from the firewall? If not, does the blower work when you have the vent or the AC on? If so, then you may just have a bad relay. There are two under the plastic cover on the firewall (2x 10mm nuts to remove). try swapping the wire harnesses back and forth to see if the blower changes. If it does, then you know at least one of the relays is bad.

Have you checked the heater hoses to see if there is a flow control valve in one of them ?

As far as I can see there is no flow control device in the hose. The AF has been replaced recently -- too many times! I have all kinds of air flow. It is just not any better than just barely warm. I think if there is a gasket under the thermostat, then I don't have one. Will go back to CTC and see if they sell it.

Thanks for the help,

Ron

Please check your Private Messages.

Checked at Canadian Tire and GM parts, and they both say there is no gasket under the thermostat. I took the thermostat out and checked it for opening. It does not noticeably open until about 205 F, so it is not opening early. I then reinstalled it with a generous layer of RTV form in place gasket material under it. Below is a graph of the temperature of the top rad hose before and after adding the sealant. It was measured basically starting from cold, and then every 5 minutes with the engine just idling. Without the sealant the hose warms up faster, which I think indicates the thermostat was bypassing a significant amount. The last data point was after about a 15 minute drive at the end of the test. Before I added the sealant the temperature while driving actually dropped about 25 deg F. Now it doesn't drop at all. Appear to have gained about 25 deg F on the air outlet temp as well. Looking like problem is solved, but will have to wait for colder weather to be absolutely sure.

http://www3.telus.net/Ron_AKA/Pictures/OldsTemp.jpg

Thanks for all the suggestions,

Ron