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No heat in cabin flushed heater core still nothing

So I have a 2005 Ford F150 4.6 V8 150,000 miles on it and the Heat will blow warm not hot just warm and after a couple of seconds it will get cold and just blow cool air if I adjust the Heat temperature switch to the coldest setting it does get colder and I can hear the blend door actuator I have tried to flush the heater core by shooting pressurize water through it with a special adpater and garden hose. The water flows without restriction and i tried flushing it in the reverse direction still flows fine. I even drianed the entire system and evacutated all the air out of the system and put a vaccum under and filled the system back up still nothing. The inlet hose to the heater core is very hot it comes out of the front of the engine but the out let hose is warm no where close to hot. At first I thought it was a restricted heater core but once I flush water through it and saw no restriction. I thought maybe they heater core valve is bad but when looking into the diagrams I couldn’t find one I was hoping maybe you guys could give me a situation or some advice I’m not an expert on Ford trucks I’m a professional mechanic for Mercedes-Benz so feel free to go technical. Thanks

It seems that heating and cooling problems would be easy for a professional mechanic no matter the brand.

I thought the same but thats why im here the heater core replacement would require removal of the dash which im trying to avoid

inlet hose thru firewall into heater core is hot. outlet hose is not hot. where is the heat going?

Its almost like the heater hose is restricted but i fushed water throw it with no issues lists one for your truck:

Heater Valve

But that isn’t proof you have one.

Remove the blend door actuator and operate the blend door by hand to see if you get heat.

If you do, the problem is with either the blend door actuator or the HVAC control module.


You have all the symptoms of a plugged heater core. Inlet and outlet temps of the heater hoses should be very close.

Just because you have flow in and out of the heater core connections doesn’t mean the core isn’t plugged. The inlet and outlet are on the same side of the core. The “honeycomb” could be completely plugged and you’re just flowing coolant in and out of the same side tank without circulating anything through the core.

I think you have to have at least some of the core tubes open to pass coolant.


Or maybe not.

Thank you ase master i think you have the best ansser that makes sense im go ahead and replace the heater core right now in the north east were feeling it so i think the heater core replacement will do thanks

Why have you not talked to your fellow professional Mercedes mechanics for help?

On your picture, you can (barely) see the line on the end tank where the internal divider is between the inlet and outlet chambers. So you’re saying this divider has corroded away? If so, the inlet and outlet hoses would both be hot.

I’m sure you’re being sarcastic . . . if so, I approve :+1:

That said, you don’t have to be affiliated with any particular car brand to properly diagnose a plugged heater core

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I’m not sure there is a divider in the side tank. The OP states he has good flow when trying to flush the core yet when the truck is operating the inlet hose is hot and the outlet is cool. That certainly points to a restricted heater core.

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If the heater core was plugged but the coolant was able to circulate around it without exchanging any heat then the outlet hose would still be hot. There is something else going on here. As a disclaimer, I have never been a professional mechanic but mechanical systems don’t defy logic or physics.

The only thing that makes sense to me is a blend door problem.

I much preferred the heater systems of the 60s and before where the temp of the heater was controlled by a water control valve and when it was shut off NO heat entered the cabin.

Why don’t you offer to buy a meal for a Ford mechanic to pick his brain.

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The thermostat was never mentioned. Also, the coolant may not be flowing through the heater core for reasons other than the obvious. The thermostat may be the culprit if you get half the normal amount of heat when the engine is fully hot. You can check the position of the shutoff valve but the insides may be broken, but if the lever doesn’t move when vacuum is applied or let off, replacement is the cure.

Once, I got a heater to work by jacking the front of the truck. Once, but it almost never helps. Then there is the worn out water pump impeller vanes which I have never found to be the cause. Other people have but usually it causes overheating. Good luck with it.

Yes,pleasedodgevan reminded me, air in the heater core could cause your symptoms. Either park facing uphill or jack the front of the truck until the top radiator hose is much higher than your heater core and bleed air out by loosening the hose clamp and sliding a small screwdriver under the hose clamp at the rad

If the input to the heater core is hot, but the outlet is at best luke warm, that might mean there’s no coolant flow through the core when the engine is running and the heat is set to max for some reason. Easy enough to determine by experiment. Loosen the output hose at the fire wall. Does coolant pour out of that hose in great volume with the engine running and the heater controls set to max heat? Suggest to do that experiment before considering to replace the heater core.