Studying up / FIXED now

Today, was a right pretty afternoon, we hauled household trash to the dumpster and picked up our supper, then rode back roads for an hour or so, saw maybe 30 deer, more squirrels, a dozen turkeys, some donkeys, horses ... and cows too. It was in the mid 50s, but I tried the heat anyway, to test for if I still had an issue, Well, no sign of leaks at the connections but still, a little mist started forming and the odor of coolant was coming back. I went under the hood at the dumpster lot to shut off both heater hose ball valves, so hot coolant can't circulate through the core.

I know that last year when it was bad that day, I could see liquid trails leading down the outside of the big box from the heater hose bibs. Earlier this week (29th), when it did it, I could see the same trails, but not nearly as much. After getting home, I redid the clamps, let the truck run awhile, no trails, no smell. Maybe sitting still with no draft pulling air through it was why it didn't mist? Today, still no trails but I was driving and dash vents were a little open, and maybe was air being pulled across some prior spillage in the bottom under the heater core. AF mixes don't dry so fast.


Just occurred to me. I could just disconnect the two heater hoses and plug one hose bib and use my handy pressure/vacuum pump to pull a high vacuum on the other hose bib and see if it holds a vacuum.
I can also put about 13 psi on it and watch for a pressure drop.
A) ... If it does hold, maybe was just residual remains of coolant from that suspected hose leak in the AC evap housing? Might be a way to flush it clear, pointing truck down hill and pouring clear or soapy water through evap core door or in past heater hose bibs until it runs out the drain tube.
B) ... If it doesn't hold, I guess I'll be swapping a heater core this week,


If it turns out I need to replace it ... and since I don't need the evaporator any longer, I'll just pull and pitch it. Probably put a critter screen of expanded aluminum there at that air intake. I have a known tested good dent side Bronco heater core on hand. I'll close off hose passageways for the AC hoses too. I put it all in long ago, I rekon I can get this done in a couple afternoons, maybe sooner.

Next day .... these red hoses that are 20 years old are OK, have a black inner, and no cracks. I examined them really close, and even today noticed the clamps at the heater core bibs weren't as tight as I thought, I was maybe hesitant to tighten them too much the other day, didn't want to deform the copper tube hose bibs. Today, I made a copper/brass adapter that lets me connect my newest hand pump that does both vacuum or psi pressure (or my old Mighty vac)to a 5/8" hose bib.
I've tested it today

• first at 20" vacuum, it held steady for 20 minutes.
• I then pressurized it first at 10 psi for ten minutes,
• then at 14 psi for ten more (has a13 psi rad cap)

and it held steady all tests. I have ball valves on both hoses so is easy to totally isolate the heater core.

• It's been setting up just above 21 inches vacuum now for 45 more minutes, I'll bet it's steady.

So my core is OK ... was probably where I just didn't have the clamps tight enough. Those spring clamps exert constant steady clamping force in a perfect circle. Got some coming. I'll go and get some different new hose, at least look at it. The old red hose is USA made. Bottom line is my old heater core which was originally in a '73 F-150 is still OK. When I put AC in in the '80s, I stripped two trucks, the '79 heater core leaked then when tested in a bucket of water and 10 psi. I'm gonna look at some pics to determine where to circle cut a 3/4 inch hole to pour a flush of soapy water into the housing to flush residue out the drain.

And to wrap it up, .... That vacuum had not budged off 21 inches and it was actually over an hour. I cut a 3/4" hole in the evap housing and poured a gallon of water in steps using a curved funnel, pour, listen .... it was coming out the evap drain. I also poured some Simple Green cleaner in there, followed by more water, checking between pints in the floor and finally, it was clean. Started the truck, opened the ball valves, set defrost to high, hot .... and got a mist for a few minutes, but there was no smell of AF .... then the mist cleared. It was picking up vapor with warm air blowing through the housing that had a wet floor. It is fixed, but I'll still use those spring clamps.

 

Today, 16 days later, it was cloudy, cool, and some light rain, and I took the '77 to go to another retiree luncheon. About time the truck was warmed up, I turned on defrost to get some warm air going, and there was a mist forming, not heavy, but visible and again, a faint odor of coolant. Pulled over, shut the valves, drove on. Get home later, leave truck running, open valves, turn defrost on high, warm, misting starts again. Left it running while I go change my clothes, come out, NO mist. None, nada, zilch! It's getting pretty warm in the truck, but no mist or smell of coolant now.

All that testing above, flushing the evap housing, no signs of leakage. It's a frustration, guessing all I can do is more flushing through that hole I put in.

Later .... I was sitting here thinking I could smell a very faint odor coolant here in the house, and I had not touched coolant today, and the truck is outside in the driveway.

Then it dawned on me, I was wearing an old work shirt that I changed into after coming home, but it is a messed up work shirt and likely I did have it on when was messing with those clamps and put that new block heater hose bib in. So I went and got a clean shirt, whiff I was smelling is all gone. I didn't have it on earlier today while we were driving down for luncheon, but I and wife both smelled a faint odor in the truck with that mist, I'll bet is still some remnant of coolant in the evap box.

Maybe a flush with gallon of soapy water or baking soda water mix through that 3/4" flush hole that I added?

11-19-2025, flushed housing update: Put that shirt on today to avoid dirtying a clean one, wife smelled AF almost immediately. In total run a gallon of soap mix and another two gallons through the 3/4" hole I added to let it drain and escape out the bottom evaporator housing drain. It'll sit for at least a week now.

 

Since the last update above in November 2025, the '77 has only been started a few times, like to move, etc. I have twice let it run long enough to get heat, both times I could see a very faint mist appear on the inside the windshield when set to defrost, warm air, felt "moist", but there was no smell of antifreeze when a rag or my hand swiped it and held close to my nose. Today, I did it again, and after warmed, turn defrost on and set fan to high. after a few minutes I could see a really faint mist so I wiped my finger on it, held it to my nose then, just was warm air, no smell of coolant. After a few more minutes, it cleared. When set to floor heat, just warmth. No smells.

I think might be still damp someplace in there where I poured stuff through the 3/4" hole I made to use as I try to flush out the coolant that I know had leaked in past the two heater hose pipes. I'm close enough to Spring to believe it'll be really dry in there by next Fall.

If I knew I could cut a neat & easy to plug 2" hole without weakening the housing or damaging the core hidden behind it, I might would.

UPDATED to say, I did do the 2" hole, see below.

 

Today is a cloudy damp day, light showers. I took my wife to go get some stuff up the road, and I was wanting to try the defrost / heat out, and put a few gallons gas in it. I checked, the ball valves open still where I left them a week ago.

We start out north, and by time we hit Rt 11 the truck was warmed up, I turned defrost on, temp on high, fan on high, W-shield started fogging up but was no smell of coolant at all.

I cut defrost off, moved temp to lower so heater valve closed, opened my window a little, it cleared.

I get home, she went in the house, I parked the truck and tried the defrost on cooler setting, very faint mist. Pushed temperature warmer, it misted more, yet was no odor of coolant. I wiped it all after the windshield was totally misted, NO greasy residue, and the micro fiber cloth had no odor even afterwards when damp.

All the testing above in #48 tells me the heater core is NOT leaking. I would have thought any just water moisture in there would be dry by now. I guess I'll give it a longer drying period, but it's frustrating.

It does seem to mist more driving rather than just sitting, so might be something at play that I'm missing here. I notice that it starts directly above both driver and passenger side defrost vents. I'll try it on a cold clear dry air day.

 

Today, between rain showers, after my tread mill time, looking in a tool drawer .... there was a 2" OD hole cutter, and a larger 2-1/4" one which measures close to 2-3/32" inside. I went out between showers, used my little finger in that 3/4" hole to feel for features, then I decided to put that 2" hole in overlapping it, just cut slow and soon I has able to gently lift the center out. I had some plastic plugs that were 2", but that would let it fall in. I cut a larger circle from a piece of aluminum using the larger cutter, at 2-3/32" it will not fall in. Tape to gently snug it up, string is just to keep it near by, and now maybe can get it dry in there. I'll make a fancier non retroreflective plug later, or paint this one black. I know I can put a shop vac in/on the hole and move air in or out to dry it out. I might temporarily stick a screen over it in warm weather to assist in drying while keeping rodents out. I already knew from the 3/4" hole is a heater core door there inside, so I missed it. 1973 era heater core is looking OK from out here.


Yeah, it's cut from a piece of old road sign the local highway shop discarded after replacing it. I just took a couple pics in case someone else needed a hole. I might make a better looking one, include a Ford oval on it too? I wonder what will take the chynah looking script off those two ball valve handles?

 

And just as a warning, there is a door in there that is moved with the cable above ... pushing or pulling on the lever. Right now it is just barely in view at the left edge of that round hole, and in use it only goes further left in the picture below, away from the hole, but you would not want to make the hole any further to the left either.

I know .... "who would?" ... right.
If not for knowing there is moisture in there somewhere that is either leftover from a hose leaking or from my attempts to wash it out, I would not have either. I know for a fact, the heater core is NOT leaking.
Hoping is just this below, will try closing the drain Sunday as gonna be cold, rainy, or snow too.
Maybe I solved the "Misting Glass Mystery" ? - Ford Truck Enthusiasts Forums