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mymove
12-30-2007, 06:41 PM
I now have about 168K miles on my '92 S-coupe and the heater is beginning to blow cold air after it idles for about 15 seconds. The temp gages reads right in the middle and if I bring the motor up to about 2500 rpm, the heater air again becomes hot. I'd like to think it's simply a waterpump/thermostat issue and not a heater core issue. Am I correct in this assumption? Remember, all this happens after the car has been sufficiently warmed up.

Thanks for all your help.....

Bill

David Neibert
12-31-2007, 12:04 AM
Sounds like it's low on coolant and has an air pocket in the motor and heater core.

David

Flex
12-31-2007, 12:26 AM
David is right. Unfortunately sometimes that air pocket arises from coolant leaking past the head gaskets. A warning sign that the hg's may be getting ready to go.

mymove
01-02-2008, 10:46 AM
Whenever I add coolant (which is very seldom), I always open the vent which rises from the top of the motor. Isn't that the very purpose of the vent.....to prevent air pockets?

Bill

mywhite89
01-02-2008, 11:39 AM
well, if the coolant level is fine,then you may have a restriction through the heater core. You may want to back-flush the heater core and see if that helps.

mymove
01-02-2008, 11:54 AM
Yes, I'm leaning in that direction. But did I mention that the temp gage slowly climbs at idle? Can the vanes on the water pump simply erode over time to the point where they're no longer functional below, say, 1500 RPM? I'd like to think a back-flush would help, but don't want to waste the money just to find out that its the water pump. Is there some tool which will test the performance of the pump? Flow meter or some such thing?

Thanks,

Bill

mywhite89
01-02-2008, 01:15 PM
Yes, I'm leaning in that direction. But did I mention that the temp gage slowly climbs at idle? Can the vanes on the water pump simply erode over time to the point where they're no longer functional below, say, 1500 RPM? I'd like to think a back-flush would help, but don't want to waste the money just to find out that its the water pump. Is there some tool which will test the performance of the pump? Flow meter or some such thing?

Thanks,

Bill

It's possible that you have blockage all throughout the cooling system. I have never heard of our waterpumps failing that type of way. Seems very unlikely. I had to replace my radiator last year for flow purposes.

Flex
01-02-2008, 03:56 PM
There are radiator shops that can power flush the system if it is blockage. This involves the addition of a caustic solution to breakdown buildup and then forcing very hot water that is under high pressure through the cooling system.

Generally though, when the system is blocked, it will make very little heat period. The only time I have ever seen the symptoms you describe is just prior to the head gaskets blowing (three times). My high k LX just started doing it this year.

You add coolant and bleed out the air but as it seeps into the motor and is burned out the exhaust, air pockets form in the sytem.

garsc
01-02-2008, 04:16 PM
It might be that you have a vacuum leak to the actuator that controls the blend door behind the dash. My experience is when motor speed changes outlet temp it is a control problem not a coolant flow problem especially if the temp change is fairly quick. Motor speed will change vacuum available to these actuators and change duct temp. Also a bad or no vacuum check valve can also cause problems.

Flex
01-02-2008, 04:20 PM
Gar,

Where would you find this bad or no vacuum check valve?

garsc
01-02-2008, 05:29 PM
The check valve is located on the vacuum suply line between the vacuum tank and the engine on my 94 its is located near the vacuum tree under the wiper cowl on the firewall.