heater blows cold air

[Libby]

This is my first post, so be gentle with me. My baby is a 67 coupe that I've owned (and driven almost daily) for 28 years. She's never been warm-blooded, but several months ago the heater started blowing nothing but cold air. My mechanic seems to think the problem is in the plenum, but isn't too crazy about the idea of crawling under my dash to work on it. I had him replace the thermostat, which made no difference. The heater core is 2 or 3 years old. I had the fellow at the radiator shop look her over, and he said the upper rad. hose was hot, and the lower "sort of hot", which he said was ok, and he didn't think the system needed flushing.
There's a lot of air coming thru the vents, it just isn't even remotely warm. It isn't cold enough to be outside air, so obviously it's coming thru the system. The temp. gauge still hits the same spot on the dial, so I would assume the engine is heating up the way it should. No coolant leaks anywhere, and the level is right. The heater box & plenum are original, & the box is in rough shape. Would a bad plenum allow only cold air to come thru? My thoughts are maybe the heater core is plugged or faulty. Maybe there's a kink in a hose somewhere, but where do I look? I hate to go to the expense & trouble of replacing the box & plenum if I don't have to. Any suggestions on what I should try next? I live in the midwest, and believe me, it's cold in that car!
I don't know that it matters, but the last work I had done before this problem started was a basic oil & filter change, and new shocks installed.

[KiltedBanshees93GT]

Well, I'm far, Er,no wait..FAR from an authority, but it seems like you should be getting nearly the same temp on the cores output hose with the heat turned off. Maybe some of the cooling tubes are blocked.
I would see if theres anyway to get to the core without yanking the whole assembly, and see how it feels while running at temp. First step is removing the glovebox, but after that?? (I dont know how similar your year is, and havent tried taking mine arpart either, sorry)

Hope its of some help, and BTW, Welcome to the board.

J

[Elvis]

I probably have very little to contribute but in my view there are a couple of things you could check. My '67 has factory air so the set up may be different. There should be a water control valve on the passenger side near where the heater hose goes into the fire wall. If you have a vacuum problem this valve may not be opening up. That would not allow the hot water to reach the heater core. It is quite simple to take the bottom of the plenum off (at least on mine it is). You can then check on whether the heater core is getting hot. I think that if the core is a problem you will usually get a leak. Also, if you do have a vacuum problem it is possible that the correct doors in the plenum are not opening. I will watch to see if some of the real experts have any better ideas. E.

[rwhite65]

The doors on my 65 are cable operated, do the doors sound like they are operating properly?
Ryan

[Libby]

Thanks to all who have tried to help with this chilly problem. First, I know there is no leak from the heater core, as this actually happened a couple of years ago, leading to the core's replacement. When I'd use the switches (yes, they're cable-operated), I could hear the little doors in the plenum open & close, so I know they were working ok. Unfortunately, I decided to double-check the operation for myself yesterday & once I got my fingers inside the plenum the whole thing literally fell apart! (why in the world did Ford use cardboard?) Talked to my mechanic & told him one of you nice people had suggested a vacuum problem, which he decided could very well be what's going on. Since the plenum is shot, he's going to go thru the system from radiator to switches, replace the necessary parts, and cross his fingers. Hopefully, I'll have heat before summer! Libby

[Phillyfanfrombirth]

You mentioned the temp of the radiator hoses... but didn't mention anything about the temp of the heater hoses...

???