heater problems
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New User
Joined: Nov 2010
Posts: 8
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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?
Hotshot
Joined: Jul 2005
Posts: 11,931
Likes: 180
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.
Elder User
Joined: Jan 2008
Posts: 973
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From: Gatineau, Quebec
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!
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!
Thread Starter
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New User
Joined: Nov 2010
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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.
Senior User
Joined: Jun 2009
Posts: 207
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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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More Turbo
Joined: Apr 2009
Posts: 657
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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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Elder User
Joined: Jan 2008
Posts: 973
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From: Gatineau, Quebec
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.....
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.....