Poor heat from both heaters

ANDY 47

MEMBER
2001 FORD EXPEDITION
V8
2WD
AUTOMATIC
168,000 MILES

2001 Expedition 4.6L. Heat was extremely hot but suddenly it stopped. Both front & rear blow luke warm. Replaced thermostat twice, replaced radiator, replaced water pump. Blend doors work because it changes from cold to warm. Hoses at the fire wall are all hot. No leaks or odors inside. What is common to both heaters to cause this problem?
Thanks.

7 Replies

JACOBANDNICKOLAS

MECHANIC
109,747 POSTS

If both heater core hoses are hot, the blend air door sounds like the problem. If it isn't fully opening, you are going to get a mixture of hot and cold air. Thus, your heat is warm and no longer hot. Check to make sure the door is fully operational.

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Tuesday, January 18th, 2011 AT 8:49 PM

ANDY 47

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4 POSTS

If it is the blend door, why do I not get heat out of the front & rear? The temp turns cold when turned to cold & only gets slightly warmer when going to hot. As the rpms go up, the heat increases some what.

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Tuesday, January 18th, 2011 AT 9:29 PM

JACOBANDNICKOLAS

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That is a good question. However, if both heater core hoses are hot, then the coolant is flowing through the heater core and should produce heat unless there is something stopping it from coming into the vehicle. The only thing left is the blend door. As far as the RPM's, you are forcing coolant through the system faster (hotter). If you didn't tell me both heater core hoses were hot, I would question an air block, but that wouldn't make sense now.

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Tuesday, January 18th, 2011 AT 9:33 PM

ANDY 47

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4 POSTS

Is there an easy check for the blend door? Should I do a complete flush with a kit first?

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Tuesday, January 18th, 2011 AT 10:33 PM

JACOBANDNICKOLAS

MECHANIC
109,747 POSTS

I would say no to the flush. Based on your description, it sounds like the coolant flow is perfect. As far as the blend door, there really isn't an easy way other than taking things apart to access it.