I have a 97 Expedition XLT, 4.6 liter - When set on heat, the air from the vents will not get hot, only lukewarm, regardless of how long the engine has been running. I had a small coolant leak and overheating problem this summer, but that is repaired now. I flushed it and put a thermostat in it then. Could I have a blockage in the heater core? As I say there is no evidence of a coolant leak. Also, how hard is it to replace the core if it is faulty?

 

After engine has warmed up touch both heater hoses where thet enter the core(under hood passenger side) see if the temp is about the same if they are both hot to very warm coolant is flowing through the heater core if 1 is much colder than the other the core may be clogged,if both are hot to warm but no heater output the problem may be a cracked blend door (where the blend door motor goes in)or a problem with the blend door motor or switch changing the heater core or blend door is a job for a pro technician the entire dashboard must be removed about 7 to 8 hours labor! I have did A/C evaporator cores as well as heater cores on Expy/F150 many times as I am a Master Tech. do the heater hose touch test 1st then we can detirmine the next step in diagnosis.

 

I'll take a swag and say that your temperature blend door is broken. Search in the HVAC forums, there'll be more details there.

 

I just today replaced a blend door actuator on a 99 F150. Wasn't to hard on that one, about 45 minutes or so. Part is like $58 from Ford.

 

Thanks for the advice, folks - I'll try the heater hose test and let you know - sounds like the blend door/heater core job may be better left to a professional! I looked around under the dash and couldn't identify anything that looked like the culprit - if I can see it, I can usually fix it, but I hate to disassemble a bunch of stuff and not be able to fix the problem...

 

need some instruction on how to put in a heater core.