Ok my fan works, but for some reason it only blows cold hair and no hot air, what would cause this to happen? and how is it fixable?

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66 Plymouth Valiant 2door. Slant 6 225, 3speed

Feel the two rubber heater core hoses under the hood - after the engine is warmed up they should be hot enough to scold you if held on to for more then a few seconds.

If one is hot but not the other, then your heater core is plugged. No water flow = no hot air. If both are hot then something is wrong with the heater box doors itself. The earlier years had mechanical linkages between the levers and the doors. Maybe one of the cables got kinked or slid out of place, or the doors are frozen solid in place. If you have the later vacuum type actuated doors, one of the vacuum pods could have developed a leak.

Alright I will be checking all that, thanks for the help

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66 Plymouth Valiant 2door. Slant 6 225, 3speed

Also there is a small hose, about 3 inches or so in length that connects the water pump to the head. I've seen a situation where this hose was missing and both nipples had plugs on them. The engine would run fine but you couldn't get any hot water to the heater core this way.

You can check the blend doors easily by removing the glove box and then working them by hand. Just be careful to not bend the cables that connect the blend doors to the heater controls in the dash.

I've seen heater cores fill up with crud. Checking the heater hose temps will find that. Chances are you may need a new heater core.

Mike

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Recognized by US Federal Courts as a Fuel Economy Expert!

try flushing/back flushing heatercore

How do i flush it? Just pull it out and stuck a house in it? Or something like that?

Also, could a plugged heater core cause overheating?

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66 Plymouth Valiant 2door. Slant 6 225, 3speed

They sell kits like this that allow you to put a fitting in one of the hoses, attach your garden hose, then use garden hose pressure to flush everything. It comes out the top radiator tank, hence that yellow plastic neck to allow you to direct the output flow
Not directly, no. You could bypass the core all together and still have a perfectly functioning engine. The thing is, if there's that much junk circulating in your heater core its probably circulating everywhere else and clogging other things such as passages in your block and radiator core. That will cause overheating.

Some (all?) blocks had a coolant drain in the block itself. It is near the oil filter, above and to the left if your standing facing the filter itself. If you open it a strong steady stream of coolant is supposed to come out. In some cases you'll get 0 coolant because its plugged up solid. You can use a coat hanger or the likes and bust through all the crud to loosen it up.