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heater problems

Old Nov 3, 2010 | 05:57 PM
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heater problems

I have a 98 f 150 with 4.2 v6 with five speed manual. My heat only works when the rpms are very high. In normal driving conditions only cool air comes out. But if u put it on the floor in second gear it will start heating. Any idea what my problem is and how to fix it?
 
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Old Nov 3, 2010 | 06:04 PM
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sounds like you have no water flow, or the water is cold. What does the temp gauge say ? Feel the heater hoses, are they hot? It might be time to take the hoses off and blast a garden hose thru and out the other side to see if you have pluggage.
 
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Old Nov 3, 2010 | 06:10 PM
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Temp gauge is running normal and lines are hot.
 
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Old Nov 3, 2010 | 06:14 PM
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I concur with steve...
You are not getting flow through the heater core for one reason or another.
Possible causes could be very low coolant, blocked heater core, air trapped in system.
Do check the hoses to the heater core to see if they are hot.
Let us know what you find.


and welcome to FTE!
 
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Old Nov 3, 2010 | 06:18 PM
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Has any work been done on the cooling system at all?
..to me it sounds like low coolant or an air pocket.
 
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Old Nov 4, 2010 | 06:09 AM
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Both lines are hot. Back in the late spring I had AC problems. My AC was working fine until I would accelerate hard and then it would turn strait to heat and AC wouldn't come back on. So for a quick fix I put a valve in the in line so could turn heat off. Then AC was working. Now that its cold I opened the valve the heat want work until I accelerate hard and run up rpms very high.
 
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Old Nov 4, 2010 | 07:08 AM
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Sounds like the heater core is partially stopped up. Because you ran with no flow thru the heater core this summer, the coolant sat in there and probably some junk settled out. Remove both hoses and flush good with water. Maybe it will open back up.
 
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Old Nov 4, 2010 | 08:06 AM
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I would check blend door motor too becose is so easy. Maybe vibrations (high RPM) move blend door motor or alone blend door that are disfuctional.
 
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Old Nov 4, 2010 | 09:04 AM
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The blend door motor is working. But not sure about the door itself. Thanks for all the advice
 
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Old Nov 4, 2010 | 09:37 AM
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Have you checked for blockage? ..or to make sure that you have flow.
Your heater hoses should get hot, and at least your upper rad hose should not be hot until the thermostat opens. Perhaps the thermostat is not functioning properly or is in wrong. Something is amiss somewhere.....
 
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Old Nov 4, 2010 | 09:48 AM
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another thought.....rotation of water pump???
I've heard of issues due to this but cannot remember what generation of trucks it was related to.
 
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Old Nov 4, 2010 | 11:32 AM
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K. Thanks for the help
 
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Old Nov 8, 2010 | 03:24 PM
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I washed out the heater core and put in a new thermostat and flushed out the radiator. And still no heat. How much water flow should I have going to the heater core?
 
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Old Nov 8, 2010 | 03:42 PM
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Have you determined that the heater hoses are getting hot? If they are, then the problem is the blend door.
If they are not getting hot, you have a blockage somewhere.
 
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Old Nov 8, 2010 | 04:50 PM
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The hoses are getting hot. If the blend door is bad will that still allow the heat to work at times?
 
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