Leaky heater core, floor pan drain, both, neither?

[Birdie]

Have a gander at the rust I uncovered below the carpet. I've read just about every article on FAQ regarding this common discovery.

I would like a group opinion: do you think this was a leaky heater core, leaky floor pan drain, both, neither?

- Note the small trail of rust coming from under dash into pedal box. Btw - the pedal box has almost no rust in it.

- My car hasn't seen rain in ages

- The heat has been stuck on a low warm draft for ages and I drive this car 2-3 hours a week. The rust trail certainly doesn't seem recent/wet.

 

I don't want to put in new carpet until I know what I am dealing with.

 

All forensic guesses and subsequent next step suggestions welcomed. 

 

p.s. dry ice covering rear floor pan drains (zero rust in the rear / fun and effective project).

[TobyB]

You mean cowl drain, methinks.

 

t

 

[Birdie]

@TobyB Actually I've seen quite a bit posted about leaky heater cores and floor drain plugs but not cowl drains. However, you might be on to something.

Edited March 3 by Birdie
add pic

[Mike Self]

What to check:

1  Plugged up heater plenum chamber drain hoses (AKA elephant trunks).  They'll allow water to back up into the heater and then leak into the car's interior

2. failed seal between the heater and the firewall.  It could be the 50 or so year old caulk that's hardened and cracked, or a PO who used an open cell foam seal that will leak from day one since it's like a sponge

3. leaking windshield gasket--you'll see rust or dust streaks down the inside of the firewall way up under the dashboard.  

 

Since there's evidence of rust atop and alongside the tunnel housing, I'd first suspect #2, then #3 above.  

 

Let us know whatcha find.  And--the above is a strong argument for at least doing a test cut on the tarpaper covering the two front floor boards, preferably where the drain covers are located.  With those in place, Birdie's rust would be hardly noticeable until your foot went through the floor!

 

mike

[Son of Marty]

I think Mike nailed it it's one of those 3 things, when you drop the heater box take a close look at it's seal surface where it bolts to the cowl for water/rust trail. The factory gasket was pretty weak now days many people just make a seal using dum-dum which is a body sealer that usually comes in little rolled ropes. You apply it just like you'd do with plumbers putty.

 

Edited March 3 by Son of Marty

[OldRoller]

I second Mike's #2, heater box to cowl seal. The rust path looks identical (but more pronounced) to my 74 I recently pulled 

the heater box on. The seal had deteriorated to the point of cracked dust. Good excuse to pull and rebuild the box.

And use strip caulk or butyl tape on the flange when reinstalling.

[Birdie]

Thanks y'all.

I spent the day investigating and indeed, I was able to pull a wee bit of open cell foam gasket from around the heater box in the cowl. That definitely seems like the culprit.

 

Luckily the pans only have a surface rust and are very solid - so nothing to worry about.

I will get the heater out in the near future, rebuild and reinstall with proper butyl tape.

[Son of Marty]

That floor looks good a bit of the old wire brush and paint, I would pull the floor plugs and reseal them.

[Gordon]

When you pull the heater box, take the heater core to your local radiator shop for a pressure test and core it out if need be. 

[Birdie]

Unfortunately with the interior and dash panels out, I put the seats back in and went for a heater leak test drive... During the drive we didn't see any coolant. However, I left the heater control all the way on and the next day coolant began dripping down the passenger side firewall. What a bummer.

 

Observations / Context

- that test drive was definitely the longest I have ever run the heater. I'm not sure I have ever actually turned it all the way on bc I had a hunch there was a leak when I bought the car (PO "mentioned" it).

- I also left the heater valve open for at least a day after the drive before I saw the leak.

- I drive this car quite a bit - even right before pulling the interior and there was no sign of moisture (coolant or otherwise) when the carpet came out.

- However, I always drive with the heater set to 'off' there is always a low amount of nice heat coming from under the dash. I say this to emphasize that it if my heater valve is broken it should have been leaking the whole time and thus, been quite prevalent when the carpet came up.

 

Questions 

- While pulling/fixing the heater doesn't seem beyond my skillset this is by all means a rolling restoration that my daughter and I prefer to keep rolling as much as possible. Therefore, is it possible to temporarily stop the leak (heater bypass or some other crazy idea?) so that I can finish the interior and come back to it? I have no problem doing things twice - like removing the glovebox, dash panels etc. I only seem to get better and find things to improve each time I do it.

- My dream path forward would be to pull the box now, put the interior back in and make the car operable while I work on repairing the heater. I understand that sounds highly unorthodox but I really try to keep the "rolling" in rolling restoration.

 

All suggestions are welcomed.

[Mike Self]

34 minutes ago, Birdie said:

Therefore, is it possible to temporarily stop the leak (heater bypass or some other crazy idea?) so that I can finish the interior and come back to it? I have no problem doing things twice -

Easily done.  Simply connect the two heater hose nipples on the cylinder head/block with a length of appropriate diameter heater hose (available in bulk from an auto parts store).  Then you can pull the heater and work on it to your heart's content.  You do need to fabricate something waterproof to cover the hole left when you remove the heater or you're gonna get a lot of flow-through ventilation--and water if it rains.  

 

The observed leak:  can you tell if the coolant is coming from inside the heater box (it'll either be running out the lower outlet doors or from the seam where the two case halves are joined) or is it coming from the plenum chamber--especially in the vicinity of the heater control valve. 

 

If the former, yeah, the heater has to come out and be dismantled as you have a leaky heater core.  But if the latter, examine very carefully both the heater valve (they can leak when they're old)  and the little short hose that connects the valve with the heater core.  That little hose is a PITA to replace and is often overlooked when replacing "all the coolant hoses."  I was horrified to find that mine was 26 years old and hard as a rock when I went to do some heater work.  I had to break it up with a pair of Channelocks and then fish the pieces out.  

 

Let us know whatcha find...

 

mike

['76mintgrün'02]

Be careful around the plastic tab that holds the valve.  They're brittle.

 

My valve leaked into my floor pan too.  Tightening the hose clamp(s) made it stop.  Coolant got into the car because the seal at the top of the box doesn't live up to its name anymore.

 

I pulled the carpet and repainted the floor, but haven't done anymore to the heater.

 

I can relate to putting-off repairs, doing things twice and also the emphasis on keeping it on the road.

 

I'm eager to hear where it's leaking.  I hope you're as lucky as I was.  One of these years I'll rebuild that box and replace those old hoses.  

 

Tom

[Son of Marty]

You could try to find another heater box to rebuild while still driving the car and then switch them out over a weekend, then sell your old box for what you payed for the rebuildable one. If you do put down new carpet I would recommend getting a couple test tube cork's that fit into the heater  water inlet and outlet put a small screw into the outer end of the corks so the screw head sticks out a bit to catch a screw drive blade to pry them out, so you don't leak coolant on your nice new carpet.

[Birdie]

The results are back and the prognosis is the short hose between the valve and the heater core was leaking like a sieve. @Mike Self nailed it. I also had to break it up with channel locks. 

 

There is one thing to add about my predicament: the heater valve has an internal leak / does not close properly. Therefore, even with it closed (heater set to the off position), when I start the car, coolant starts shooting out of the valve into the cowl. 

 

Therefore my options are to replace the hose (reconnect the system) or plug both the valve and the heater core inlet for now. I am leaning towards plugging the system because reconnecting them means that coolant would be flowing through the valve and core at all times. There is no upside to this (I don't need heat right away) and a downside of more potential leaking. The heater/cowl seal is non-existent, so just keeping all fluids away from this area seems the safest way for me to get the carpet back into this car. Opinions? Things I am overlooking? I really could go either way on this one.

 

Then, I will come back and fix the valve (I see there are rebuild kits) and reseal the heater/cowl. Quick question, I think I know the answer, is there any way to fix the heater/cowl seal without completely taking out the heater? Now that I am fairly certain my heater is not leaking, the whole electrical, cables, etc. just make that project seem a pita to replace the seal since I don't drive in the rain, ever (California)..

Edited March 9 by Birdie
add a comma.

['76mintgrün'02]

Have you checked to see if the cable is pulling the valve all the way closed?  

 

My valve wasn't working when I bought the car.  I got lucky and found that the screw that attaches the lever arm to the valve was loose, so it didn't turn the valve.  I aligned the hole in the tab and tightened the screw and that fixed it.

 

The valves have a hole in the plate to let some coolant circulate when it is in the closed position, so that might explain why yours is letting some through when closed.  (At least the late model cars do).

 

Tom