Ok, I am new to the forum. I have a 1978 F150 4X4, 400 2bbl.

Air blowing out of defrost or floor vents never gets warm until the weather warms up some. Have pulled heater hoses and blown air through the heater core. Seems to have no restrictions. Engine temp appears fine. I have a 195 degree t-stat and have blocked the radiator by about 2/3. I have also taken the fan shroud off in an attempt to force the engine to run hotter so I can get some warm air in the cab. All to no avail.

Any ideas?

I ahve been freezing my butt off for the past few weeks in Michigan.

 

welcome to the site!
check to make sure the heat control door in the heater box is adjusted correctly and not letting cold air past the heater core. Even though you say you cleaned the heater core it may still be plugged enough to slow the heat down. I live in Michigan too, I had the same problems a few months ago, and after I replaced the core it was better than it had been in years.
Joel

 

Thanks for the quick reply. I will feel in the box to ensure the door is closing all the way. I have had this apart once before and did not notice any restrictions in the movement of the door.

How can I tell if the heater core is clogged, even partially?

 

If its clogged, one heater hose will be much cooler than the other. With a new core, both hoses feel about the same temp.
Joel

 

Is this a standard heater or does it have AC ?

have you physically moved the HEAT/TEMP control cable so it is in the HOT position?

 

Truck does not have A/C, never did.

I guess my hands just aren't sensitive enough. I really cannot feel any difference in the heat of the hoses when I grab them.

 

Yes, I have moved the cable. I have also disconnected both cables from the box, and moved both the mix door and the other door (heat or defrost) to the max both ways to determine there is no bind or lack of travel.

 

The only thing from the Ford heater trouble-shooting guide that hasn't been done or mentioned by you is :

Check cowl,Vent,air ducts for adjustment and/or air leaks (if applicable)

That's the last item in this guide.

NOTE: at normal operating temp the heater hoses (BOTH) can NOT be held on to for very long without burning ones hand.

are yours this hot ?

 

Some of the standpipe adapters on the intake manifold where the heater hose clamps on, have a shutoff valve on top like a kitchen faucet. Turned all the way in will shut off the water to the heater core. Hoses won't get warm because water can't flow through them. Rust can clog them inside too.


And then there's the dreaded Ranco Valve aka heater water control valve. Those damn things leaked, and also stuck closed. You can slide the lever on the dash back and forth till doomsday, and nothing will happen, because the mechanism on the valve is shot.

 

I can hold the hoses as long as I choose. So, apparently the flow is limited. I guess I will pull the hoses and heater core and check for restrictions of any type. I will also verify that there is no restiction from sediment/rust at the nipple in both the block and the water pump.

Thansk to everybody for helping. I will let you know how it turns out.