67 F100 - No Heat...Not sure what else to try...

[clineco]

Since I've owned the truck it has not had heat, the blower motor is strong, the pull knobs all seem to function as they should. I've replaced the thermostat to the original, just replaced the heater core, checked the inline valve going to the water pump (moves freely and is unclogged). But for whatever reason I am not getting any heat. The one problem I found is that the hose coming from the thermostat is Hot, but the line returning to the water pump is cool (I'm assuming that's the direction the water flows). Hoses all seem good too.

Anything else I can check?

[tnlprt]

Are you sure the valve is open..

Heat in No heat out

You have a blockage after the hot hose and before the cold one

Valve or heater core

[clineco]

Yep. Took the valve off and it's wide open. Brand spankin new heater core installed. The one I replace didn't look very old either and it was free of blockage...

[clineco]

Just had another look but the problem persists.

I removed the hose from the thermostat and the hose from the water pump. I was able to blow through the thermostat hose and out the other so there isn't a blockage there.

I'm stumped. Any other ideas?

[cep62]

Did you try using a garden hose and flushing through the heater hoses starting at the water pump?
A friend had a plastic flushing T that collapsed and restricted the flow.

Is there enough air flow through the heater box ? no mouse nest? no plugged cowl area ?

While the heater hose is off does water flow out of the pump? I've seen eroded water pumps that won't flow coolant.

[clineco]

Did you try using a garden hose and flushing through the heater hoses starting at the water pump?
A friend had a plastic flushing T that collapsed and restricted the flow.

Is there enough air flow through the heater box ? no mouse nest? no plugged cowl area ?

While the heater hose is off does water flow out of the pump? I've seen eroded water pumps that won't flow coolant.

All I did was blow air through both sides and everything seemed clear. The airflow blows like a hurricane so we're good there. I guess the only thing it could be is something with the water pump.

Does the water flow out of the water pump and into the heater core or the other way around? Because the thermostat hose is hot, but the water pump side is cool.

[tnlprt]

What engine are we talking about

The hose should come from the intake not the thermostat

[clineco]

It's the inline 300

[Busboy]

If your hose going into the core is hot and the one coming out is cool then you have either a blockage or an air lock. You might try bleeding off some coolant from around the return nipple by loosening the clamp and putting a screwdriver or something in between the hose and the nipple to hopefully bleed the air out. Also running the engine at a fast idle helps.

[tnlprt]

Do you have a cable hooked up to the heater control valve

If so take it off and work the valve by hand when the truck is warmed up

see if it makes a difference

[sargentrs]

Disconnect your heater hoses. Pot a short piece of hose on the heater core inlet tube. Stick a water hose nozzle in the hose and clamp it tight. Slowly turn the water on. You should get a steady stream of water from the outlet tube. If so, hook the inlet hose back up and run the engine. You should get the same stream of water that gets hotter as the engine warms up. Remember to keep adding water to the radiator if needed.

[clineco]

Old post but I thought I would follow up. The previous owner replaced the thermostat housing and in doing so replaced it with a housing for a 240 engine and not the 300. Long story short there was some holes misaligned and not allowing the water to flow correctly.

[sargentrs]

Thanks for updating us!

[1972hiboy]

Yes thanks for the update! its always good to know in the end what was a confirmed repair...... glad you hear you have heat now. truthfully I was kinda bettin for a blend door issue as I was reading through everything.