Leak from cowl into cab

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Leak from cowl into cab

rshemmy
Hey everyone,
I've been looking into a leak from when it rained a couple of weeks ago. The whole driver's side floor was wet. I took off the trim and cowl and poured water onto the windshield and into the cowl. It looks like the leak is coming from the driver's side of the cowl down low where it drains out, but since I can't see down there well I'm not sure what is going on. The leak inside the cab looks like its coming in from the firewall in the back left corner when looking at it from the driver's side seat. There also appears to be water leaking on the down from the wall below the side air vent? I'm not sure how that gets there. Any help would be appreciated on where to go from here. Thanks.
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Re: Leak from cowl into cab

taskswap
I had this exact problem. The thread is very long but if you look through the "Rocky" build thread there's a lot of good advice from other members here on it.

There are a couple of different causes and so there are a few solutions to try. My issue boiled down to two specific things. First, on the firewall about mid-way down the driver's side panel are three or four holes with grommets for various things going through: wires, speedometer cable, etc. They're prone to rotting out and in this photo you can clearly see one or two of mine with this condition. Well if you look closely just above it there's an area of adhesive where a drip rail used to be. I can't find a good photo of that, but for my year (81) I'm 90% certain there was a piece of L-channel above there that directs any water that might come down through the gap between the cowl and hood down and away from the grommets. So I had a double whammy. Any time I would drive in the rain I got water coming in here. I knew this was at least one issue because if I felt the inside of the firewall it would be wet (not just the floor).



Next, the vent in the driver's side kick panel is a common leak source. It's a very common problem but in my build thread there were conflicting opinions on the fix. One camp focused on this channel filling up with debris, especially in earlier model years where the cowl cover had slotted vents that let more debris in than the grille of smaller holes later years had. This was a good tip because it led me to find an old towel that had been stuffed into the bottom of the channel for reasons I'll never understand - it was pretty gross. But despite that being a terrible idea my channel was completely clear, it had nothing but a bit of dust in the bottom, not enough to hold water.





My solution for my particular case was to replace the gasket around the vent itself. There's supposed to be one there but at least in my era it was a lightweight foam that would dry-rot and turn to dust. On my driver's side it was completely gone, actually. If you study the shape of the vent closely you'll notice that the top edge has a lip and a curved edge that forms a sort of drip rail. Water flows freely down this channel when it rains (from the cowl vent) so the drip rail catches and directs it around the vent so it can flow out the bottom. But that seal is important because when it hits the bottom of the rail it has to stay outside. It needs a seal to help with that.

I'm pointing at a spot I had some doubt about here, so I was documenting it for myself. The original factory vent seal (I'm 90% certain) did not go all the way around. It was a U-shaped piece with the bottom edge open. That's common with a lot of windows and vents so any moisture that does build up has a way to drip out in a good direction. But I was still getting a drop or two through this bottom area and my opinion was my vent had warped a little bit with age (it's not super obvious but it's not 100% flat). I took the chance of extending the seal all the way around, and so far this has resolved the issue for me.



YMMV. Good luck.
--
1981 F-250 Custom. 6.6L V8, 4 barrel Holley carb, ARA aftermarket A/C.
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Re: Leak from cowl into cab

rshemmy
Thanks for all the tips. I will have to go check out the truck and come back with some info.
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Re: Leak from cowl into cab

85lebaront2
Administrator
In reply to this post by rshemmy
I had a similar problem on Darth, water would show up on the right side under the carpet. I finally gutted the interior as far as the carpet went and waited for our next deluge. When I saw a fellow with a long white beard loading animals on a big boat, I felt it was good enough for a test. When I opened the driver's door and got in, I could see a trail of water running from the corner where the inside of the cowl, back of the firewall and floor pan front kickup all join.

After the rain stopped, I removed the inlet duct from the HVAC system and looking inside the cavity, found that there was no sealant of any kind inside the air duct and cowl drain area. Cleaned it, dried the area and spray undercoated the whole thing inside. After it dried, it was garden hose time and no more leak!
Bill AKA "LOBO" Profile

"Getting old is inevitable, growing up is optional" Darth Vader 1986 F350 460 converted to MAF/SEFI, E4OD 12X3 1/2 rear brakes, traction loc 3:55 gear, 160 amp 3G alternator Wife's 2011 Flex Limited Daily Driver 2009 Flex Limited with factory tow package Project car 1986 Chrysler LeBaron convertible 2.2L Turbo II, modified A413

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Re: Leak from cowl into cab

Rembrant
In reply to this post by rshemmy
When the water runs down the cowl, it drains down the left and right sides of the cab through rubber "duck bill" openings. These drains get plugged with leaves and debris after a while...and then the water leaks into the cab. It's worth checking them. See pic below of my '84 I circled the drains in red.



1994 F150 4x2 Flareside. 5.0 w/MAF, 4R70W, stock.
1984 F150 4X2 Flareside. Mild 302 w/ 5spd. Sold.
1980 F150 4X4 Flareside. 300i6 w/ 5spd. Sold in 2021.
1980 F100 4X2 Flareside. 351w/2bbl w/NP435. Sold in 1995

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Re: Leak from cowl into cab

rshemmy
In reply to this post by taskswap
I put some weatherstrip around the side vent and looks like the leak is gone. Thanks for all the help!