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97 Explorer, Heat doesnt work at idle, only blows hot at highway speed >2000 RPM

(1997 Ford Explorer)
in Sparta, MO on January 16, 2018
97 Ford Explorer XLT, 4.0 sohc. Blend door seems to operate fine but only cold air blows, unless you rev motor. So, heat is there at highway speed, but you freeze at red lights, driving around town.

I suspect a weak water pump or plugged core (maybe both). Any other ideas? Thanks!
Tags: ford, explorer
Displaying 4 answers & 2 comments
Popular Answer
on January 17, 2018
Google > 1997 Ford Explorer heater control valve ... View the resulting page.
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on January 17, 2018
A malfunctioning heater control valve will produce the same symptoms as a restricted heater core!
on January 17, 2018

Below is a link to a very interesting video on the **HEATER CONTROL VALVE**

Good luck to all..!
on January 16, 2018
Air pockets can cause this, possibly from recent cooling system repair work also. Besides what Alex said.
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of Rick's Automotive on January 17, 2018
Step by step diagnosis would be to inspect coolant level. If coolant is low, refill cooling system & confirm heater operation at this point. If heat is still weak after filling system test operating temperature of engine with a pyrometer. If engine temperature does not come up to 190 degrees (or manufacturer's specification) replace the thermostat & retest. If engine temperature is coming up to normal test both heater hose temperatures. They should be fairly close in temperature. If not , inspect for a heater control valve malfunctioning (most late model vehicles do not use a heater control valve). If valve tests good or no valve exists the heater core is restricted. Back flushing the heater core may be an option.
Typically there will be engine over heating issues if the water pump impeller is failing.
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on January 16, 2018
First thing to check is coolant level when the engine is hot. If that is ok the check the heater hoses going to the heater core. They should both be hot. You could also have an open thermostat.

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