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Old 01-31-2004, 12:16 AM
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Need help troubleshooting my heater system.

Hello. I have a 1976 Chevrolet Pickup. My heater works fine once the engine warms up, but then, after i start driving around town, or just cruiseing on the freeway, it starts to blow cold air. I'm not familiar with how the blend door or anything like that works on these models. Has anyone else had this problem? Can someone at least point me in the right direction? Any advice will help.. Thank you.
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Old 01-31-2004, 08:00 AM
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It sounds like your thermostat is stuck open. I would first check it out an replace it. Can be done for a few bucks.

Kevin
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Old 01-31-2004, 08:22 AM
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Is your coolant low? If it is, you won't get enough through the heater.

Is there a temp guage? See if it drops off when heater goes cold.
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Old 01-31-2004, 10:25 AM
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well that's the thing, i have a new radiator which is full of coolant, i have a new 195deg. thermistat... I don't think the problem lie's within the coolant system... i think it has something to do with the heater controls. Are they vacuum controlled or mechanical or what? My engine temp stays constant once it warms up.

well that's the thing, i have a new radiator which is full of coolant, i have a new 195deg. thermistat... I don't think the problem lie's within the coolant system... i think it has something to do with the heater controls. Are they vacuum controlled or mechanical or what? My engine temp stays constant once it warms up.
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Old 01-31-2004, 01:25 PM
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If it has A/C, the controls are probably vacuum assisted. At least they were in the 80s. If no air, then there are just cables.

If you are getting heat when it is warming up, why would the controls change?

Have you tried flushing the heater core? But, then again, you are getting hot water... When it is heated up, see if both heater hoses are hot. If they are, hot water is flowing through. If not, there is a blockage in there.
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Old 01-31-2004, 11:30 PM
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ok, i think your right. I've noticed that one heater hose is significanyly warmer than the other. But, i figured that if it was working correctly, wouldn't the exit side of the core have cooler water going through it than the entrance hose, due to water to air heat transfer?

-carl
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Old 02-01-2004, 06:48 AM
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You might want to try back flushing your heater core.

Remove your lines and take a garden hose to the return line and let the inlet line flush out. (Reverse flow)

Do not put a lot of pressure on the flush water. Considering the age of your heater there is probably some "junk" in the core.

My son just had the same problem and you would not believe the crap that came out of his.

Just go slow and you might have more heat that before.

Hope this helps. Let us know how this works out.

Pappy
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Old 02-01-2004, 06:49 AM
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Once its warmed up, you wouldn't notice the heat diffference.
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Old 02-02-2004, 02:21 PM
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HEY CRAZIE: I had a similar problem on my streetrod. I had a hot hose going in and cold coming out. I took the return line loose a a big BURB came out. It had an air pocket that formed when I changed T'stats....Think Simple....DAVE
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