Hey there. First thread starter in this forum in a while for me.

My daughter has a 2005 F-150 XL V6. She's been putting up with low heater output lately and I finally got the chance to look at it today.

Sure enough, engine gets up to normal operating temp and there's barely any heat coming out. I turn the temp control **** over to cool and it cools down quick. I turn to heat, hear the motor turn the blending door ( no popping or clicking) and heat barely emanates. There's no cloud of radiator fluid and no drip from the heater core either.

Ideas? Heater core plugged? Blending door broke?

 

You need to clarify the symptom.

Is it an issue of diminished volume of air flowing through the system or is it an issue with normal air volumes but insufficient heat produced?

 

so you believe the thermostat is up to 190 degrees... feel the heater hoses in and out and compare to radiator top hose.. BOTH hot ? If one is cool then you don't have flow... Make sure radiator overflow tank is up to PROPER level.. Low level will trap air in heater and no heat output......... If hoses are not HOT, then pull off hose and flush with garden hose.. If both hoses are HOT, then possibly look into the blend door no moving properly.

 

I'm inclined to agree with steve(ill), both heater hoses under the hood at the firewall should be too hot to hold. If they are the blend door is broken, if they're not that hot the heater core is clogged. A backflush might clear it, if not it has to be replaced.

 

A clogged core is only one of the possibilities, there are more. I just lump them all under "insufficient coolant flow" as an initial description with additional work needed to pinpoint the actual cause.

 

Blower fan works fine, insufficient heat produced.

 

Okay that sounds like a good check. I need to drive her truck up and down the road, get it really good and hot, then check those hoses.

 

Ugh, not the best options. It's gotta be done though..

 

Real simple; water ain't hot enough or water ain't flowing through heater core. If you drive the truck until the thermostat opens and you have full temperature, set the heater and fan for full blast, stop the truck but leave it running, open the hood and grab the upper radiator hose - it should be too hot to hold. Now grab the heater hose - it should be as hot as the radiator hose.
My guess is low coolant and old coolant. Look at the coolant in the surge tank - it should be clear and gold color. If the surge tank is empty, you have a coolant leak and low coolant. its possible the heater core might still be good but you'll need to flow-test it before spending money on new coolant. IOW, if the heater core doesn't flow, fix it and then replace the coolant.
Many vehicles have a coolant valve at the heater for the purpose of keeping hot coolant out of the heater core when the A/C is in use. Could be that if so-equipped.
Anytime you're dealing with cooling system problems, including the cabin heater, remember that there are many weird things that can cause problems. We are talking here about the ordinary and most common causes of no heat.

 

Good insight there, thank you.

Ordinary and common causes are what I am hoping for. Nothing too exotic or expensive.

 

Well you can get some wild things, like hoses that break down on the inside and a flap of rubber blocks the flow, for example. Once on an old Mustang, it would get hot on the highway but was fine in slow traffic even on a hot day. Exactly the opposite of the usual. The radiator seemed to have good flow with the water hose. I removed the thermostat housing to replace the thermostat and for some crazy reason I stuck my finger down into the coolant (which was cool at the time) in the lower half of the housing and I felt something - turned out to be a rubber washer with a small hole in it, like what they call a 'fender washer' made of steel. At low flow, it stayed down in the housing, but at high flow it would rise up and block the thermostat, causing the heating. I have no idea in the world what that thing was or how it got into that cooling system but it just goes to show you to keep an open mind and don't rule out anything!

 

Got another chance to look at her truck today and sure enough, one heater hose is hot, the other cold. Next chance I get, I'll back flush the core and see what happens then.