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Feb 5, 2011 | 08:24 PM

scountryman

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No Heat

98 F-150 4.6 Heater suddenly stopped working so changed Thermostat.No help. I only get heat when going down hwy w/ OD off. Fluid level good. Thought "new" thermostat might be bad so just changed it again w/ same results.

Is there a heater control switch under the hood?If so, is it hard to change ?
Thanks for any help.
P.S. Truck has 369,000 Miles with very few problems.

Feb 5, 2011 | 09:08 PM

steve(ill)

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well, what does the temp gague on the dash say ? If it is in the normal position, then the thermostat is not the problem.. Assuming the thermostat is good, and the water is not, then your problem is in the heater or the controls. Since it is "sudden" i would guess the contol system. You have a **** on the dash that rotates hot to cold. Pull the **** off and see if it is actually turning the control shaft. Sometimes the **** hole strips out. If the shaft is turning, hit is supposes to send a voltage to the blend door motor. THe motor moves a door in the air duct that mixes hot air from the heater with cool outside air to get the desired temp. YOu might have a bad motor, broken door hinge or broken lever to the door. The motor and door are above the transmissino hump, under the radio. You should be able to remove the plastic dash section and see the motor tucked back in by the duct. MOve the heater control and watch the motor and control arm.

Feb 5, 2011 | 09:11 PM

steve(ill)

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skip down a couple posts and look at door #5 in the photo

https://www.ford-trucks.com/forums/9...-please-2.html

Feb 5, 2011 | 09:17 PM

steve(ill)

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read the last post about going thru the glove box... maybe ?

https://www.ford-trucks.com/forums/1...lend-door.html

Feb 6, 2011 | 06:45 AM

scountryman

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I'm a newbie here. Sorry i didn't fully describe the problem. Temp. gauge reads norm. water gets hot, but the heater hoses don't get hot.That's why i asked about a control switch under the hood. I replaced the heater core about a yr. ago(not my idea of fun! ).
Thanks for the reply

Feb 6, 2011 | 07:00 AM

qbenplaya00

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hows your water pump?

Feb 6, 2011 | 07:03 AM

scountryman

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seems to be o.k. water in overflow bottle moves steadily when engine warms up.

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Feb 6, 2011 | 07:06 AM

n5926g

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From: Hernando Ms

It sounds like you have a "circulation" problem.I have doubts that its the water pump,as if it were you would have overheating issues.
With that being said,My next thought will be a plugged up heater core.I know you said you changed it,but that doesent preclude trash getting circulated through it,and restricting the flow.
If you can locate the inlet,and outlet hoses under the hood,disconnect both,and run a water hose into one of them.Turn the water on slowly,and see if the approximate flow out the open end is about the same as what your puttin into it.If it is,the core is not restricted.IF however you feel back pressure,and no/little flow,you have found the problem.