Well, I'm getting frustrated. Old truck has been sitting for over a week. Today we took it up to Waynesboro, I turned on defrost with heat, extra valves open, see mist develop lightly inside the cab. Very faint, I mean very very faint whiff of antifreeze. Shut it off, and closed the valves while gassing up. Get home, leave running while we unload, valves back open, defrost on temp set to hot, NO misting now, no smell. I've tested the heater core both with vacuum and with 14 psi pressure, it held ...., tried flushing, the box twice, I did have some leakage that started this mess.
Described in post 46 & 47 https://www.ford-trucks.com/forums/1...er-core-4.html
What am I missing. Can it be that is still dampness in the floor of the AC box? Maybe I just need to forget driving it in November until about April?

 

I hate heater cores.

 

Keep driving it and see if it gets worse. Maybe its just residue from previous spillage or leak. As you noticed it doesn't evaporate well. I would use some fluorescent dye in the coolant then if you do take it apart later you will see where it is leaking with new core if it is at all.

 

Could be the hoses or clamps in the engine bay. I've seen hoses that leaked between the plies. i.e. comming out of the end of the hose. If so it will run down into the box I believe.

Watch coolant level.

 

Thank You for your comments. I had read that a great cleaner of antifreeze is rubbing alcohol, might try that too. I just don't see how the heater core held pressure and vacuum if it leaks, and I know that I had a leak at the heater core inlet or outlet pipes with the older heater hoses and am sure some of that found it's way into the big box, but these new hoses with the doubled new constant tension spring clamps aren't showing any sign of leaks there, and maybe just over the years past there is debris, dirt, dust, etc in there that has absorbed some of the AF and .... well ..... I wish it wasn't. I can push that door open for recirculating AC air and feel some mix of that trash along the bottom where would above the seam, next to the AC evaporator, so I know is likely some inside there. It's just that like .... now, think is doing OK .... then it pops up again.

I have noticed that unlike AF mix, it has misted up, then faded away with no or only the faintest smell of AF and if wiped off with a micro like wrag, it wipes clear real easy unlike the first times when it was bad.

Might help too if I just ride up the road bundled up, windows down, heat set up on high and temp set all the way to hot, on a not subfreezing day, after a bit of the alcohol treatment poured in the hole I added?

Maybe after pouring the alcohol in, an air jet pointed through the evaporator would help?

I'm gonna try thatfluorescent dye in the coolant, and if I ever see it or not afterwards, is a clue too.

 

You know if it ever fogs the windshield or smells like antifreeze you're looking at replacing the heater core.
Its inevitable so just go a head and replace it before it empties your cooling system on your floor.

My first taste of replacing heater cores was a long time ago when I replaced a friends heater core in his 1969 Mustang convertible with factor AC.
It seemed lie I was always the one that got elected to replace heater cores in the shops I working in and I have no idea why.
I did one in a VW Passat that was pure hell and ha to replace it again because the new one started leaking a few weeks later.
The easiest were Ford Ranger pickups, the little Rangers with AC. They were easier than the ones WO AC.
They only paid 0.8 hr labor.
I hated changing the one in my 1979 F-250 with factory air too.
The one in my 1976 F-250 WO AC wasn't too bad at all.

 

Oh, I can change it, but with no garage, I'd put it off till Spring. I'd be the first to have said it was a bad heater core, except that having had the leaking hoses over the last year, seeing where the leak was .... and knowing that those seals at the point where the heater core pipes exit the big box don't really seal but so well. What bugs me is that on 11-03-2025 it held vacuum for a long time, and held:

• 20 inches vacuum fore over 20 minutes rock steady
• 10 psi pressure for 10 minutes with no drop
• 14 psi pressure for 20 minutes with no drop
• 20 inches vacuum fore a little over an hour with no drop

I had the two extra added valves to shut, and so I was only testing the heater core. I have an extra heater core, it passes the same tests too, looks might near unused even though it is a OEM. If not solved when we have a warm spell, guess I will swap it.

 

I’d suspect it’s the debris and AF soaked in. If everything tests out, I’d just take it all apart and give everything a twice over wipe down with alcohol. Follow up with something to recondition the plastic or rubber (WD-40?).

Like you said, it’s probably just a bit of AF that keeps getting “reactivated” by condensation.

 

I was looking on line and what lead me to consider alcohol was a suggestion I saw somewhere for a guy in a discussion that paralleled the suggestion that "condensation of water, or just water, can do that, since the water was the first part of the mix to evaporate". Most of us have had AF mixes spilled in a driveway and something often stays there until a good rain or a lot of water is sprayed on it to wash it away.

I do think it's getting better. I am glad I added the two ball type valves.

You mentioned condensation, and I had not considered something. When I think is OK to turn on, to add heat, often is after we just left the house, is cool coolant in a cool heater core when I first started out, is not circulating as it warms in the engine as the vacuum operated heater valve is still shut, even if I have the ball valves open. Then suddenly I turn the heat or defrost on, blower starts, and when I move that heat control towards warm, the heater valve opens and the warm coolant starts moving into the core .... but that heater core metal is cold still as is the coolant in it back to the heater valve, so it's not instantly hot. Heater blower is moving air from the cabin or outside, but it's cold air at first being blown through the core that's not yet hot. I don't get the mist but right at first, and it does wipe off with no greasy residue .... but it carries a faint odor off the soaked debris maybe.

A while back I took my Wife for a shot, tomorrow she has another. Last time was a cold day but after a 20-25 minute drive, the engine was heated up good. While she was in the Dr.s office, I kicked the defrost on max, run the blower on high, temp on max heat, and I got hot, almost fell asleep, but there was then no mist and no smells. I was might near sweating time she come out. I'm gonna try it again tomorrow.