The All Too Common Heater Problem
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Elder User
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From: Coleman, Wisconsin
The All Too Common Heater Problem
My heater stopped blowing heat about a month ago. I parked the truck last week to see what the problem is. Heater core was replaced last fall. Both hoses are HOT. Fan blows good. I took the heater box out tonight and the core is fine(not plugged), and the door shuts fine. Now what else is there that could be stealing my precious heat from me???? I'm getting frusterated. I'm pretty close to junking the hole thing and getting a mojove heater.
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From: Virginia
Here's my long road to finally getting my heater to work so good, it will run you out of the cab.
1. I got all the pencils, watches, papers, and junk out of the duct at the windshield.
2. I plugged the holes in the cab. This inlcuded rusted out cab corners, ripped shifter boot, and doors that where not shutting correctly.
3. New heater core
4. Cleaned out the old A/C core and got the junk out of the flapper door behind it.
All of the above yielded small improvements, but #4 made the biggest difference.
1. I got all the pencils, watches, papers, and junk out of the duct at the windshield.
2. I plugged the holes in the cab. This inlcuded rusted out cab corners, ripped shifter boot, and doors that where not shutting correctly.
3. New heater core
4. Cleaned out the old A/C core and got the junk out of the flapper door behind it.
All of the above yielded small improvements, but #4 made the biggest difference.
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Elder User
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From: Coleman, Wisconsin
Any more theories?? All those steps have been done before but still nothing. If I turn the fan off for a few minutes and then turn it on low, a small amount of heat will come out but then go back to cold. Could the gap between the fan blade and blower motor be too big causing this to happen??
More Turbo
Joined: Mar 2002
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From: Easthampton, Ma.
If both heater hoses are hot, that means the heater core is hot!
If air is blown thru a hot heater core, the air will come out hot!
Are both heater hoses remaining hot when the air coming out of the heater is cold? This indicates the air is bypassing the heater core! Possibly indicating an improperly positioned diverter door in the heater.
Is one hose becoming noticeably cooler when the heater blows cold? This indicates poor water circulation!
Let us know.
Steve G.
If air is blown thru a hot heater core, the air will come out hot!
Are both heater hoses remaining hot when the air coming out of the heater is cold? This indicates the air is bypassing the heater core! Possibly indicating an improperly positioned diverter door in the heater.
Is one hose becoming noticeably cooler when the heater blows cold? This indicates poor water circulation!
Let us know.
Steve G.
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Elder User
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From: Coleman, Wisconsin
I checked the heater door and it worked perfect. Both hoses remain hot all the time. I don't notice one getting cooler than the other, but I'll go out and check for sure in the morning. If I had poor water circulation to my heater core, wouldn't the engine run hotter too?
More Turbo
Joined: Mar 2002
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From: Easthampton, Ma.
No, you can completely block off the flow to the heater core and it will not affect the engine temperature (not noticeably)
Is the "blend door" (the one that regulates the temp) going all the way to hot, sealing off the cold inlet?
What year, make and model truck?
What engine?
a/c or non a/c?
Steve G.
Is the "blend door" (the one that regulates the temp) going all the way to hot, sealing off the cold inlet?
What year, make and model truck?
What engine?
a/c or non a/c?
Steve G.
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Elder User
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From: Coleman, Wisconsin
Blend door is sealing. It's a '81 F100, 300-6, no a/c. I'm going to put new hoses on today and if that doesn't work then there must be something with the water pump, I think.
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Elder User
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From: Northern MD
My cousin had this problem with his car some years ago. I removed the heater core and flushed it in both directions. What came out looked like rusty Jello pudding. If you're going to replace the hoses, remove the heater core and flush it out. You've obviously got a flow problem with the core. Water's flowing through it, but not at a great enough rate to stay hot once the fan starts blowing at a higher speed. If you don't want to flush it, you can replace it. But flushing's a whole lot cheaper. 
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Joined: May 2004
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I heard what you said, but all signs point to a blend door problem.
If you've got hot water running into the core, you'll get heat, unless cold air is being introduced. Does someone know how to test whether the blend door is working properly, and I don't mean "I hear it"?
If you've got hot water running into the core, you'll get heat, unless cold air is being introduced. Does someone know how to test whether the blend door is working properly, and I don't mean "I hear it"?
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Joined: Sep 2002
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From: Reno usa
Is it actually blowing cold air? I mean a good flow of "cold" air or just a trickle of cold air even though the fan is humming away?
Are you certain the squirl cage is turning?
You might check you wiring - it could be that it is backwards and the fan will be blowing the warm air out the --- in.
Or its not turning at all even thought the motor is.
Just a thought......
Are you certain the squirl cage is turning?
You might check you wiring - it could be that it is backwards and the fan will be blowing the warm air out the --- in.
Or its not turning at all even thought the motor is.
Just a thought......
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Elder User
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From: Coleman, Wisconsin
Yes it blows cold air. Not as cold as the outside air but still cold. I flushed the core both directions, nothing but water came out. I must have spilled coolant in the box before I put it on because now all my windows are full of that antifreeze film. Its just one thing after another. The hamster wheel turns great and is blowing in. I also 'looked' and the door and it closed right tight. If I don't get it fixed during my week off, I'm ripping the hole box out, blocking it off, and putting a nice simple propane heater on my floor. Maybe if I die from lack of oxygen I won't be cold anymore. I don't know what else to do other than water pump.
Last edited by Boss50; Dec 22, 2004 at 09:48 PM.
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From: Virginia
The waterpump is going to be a waste of time. The engine would overheat if it was something wrong with it. Does your temp guage work? I am wondering if your thermostat on the engine is working. You would think it is working, since you said the hoses were hot. They should be hot enough to where you can't hold on to them without burning your hand. Are they that hot? You may want to compare them to another vehicle you have.