heater blew nothing but cold air that evening

FORD F-150
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MIKIE
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I replaced the stat in my '97 Ford F150 - 4.6L. The heater worked perfectly the next morning. It blew nothing but cold air that evening and always since. Other than possibly having the wrong stat or a defective one is there any other reason I would have this problem not withstanding a clogged heater core (which it's not). by the way I tried to donate to your cause but the link didn't work (some kind of error).
Feb 5, 2007 at 7:05 PM
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MIKE H R
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try starting the engine when its cold. holding the hose closest to the thermastat. the hose will stay cold until the thermastat opens. you should feel a sudden temperature change. means the thermastat working properly. if the temp rises slowely than may be a stuck open thermastat. have seen new ones that were bad. if the thermaste works ok then the heater core might be vapor locked or clogged.
May 10, 2021 at 10:36 AM