Advice needed about Cowl treatment

[9Fingers]

I've slowly been at work removing the interior, instrument cluster, radio, heater, and finally the firewall insulation. The issue is water in the floor after a rain. I have borrowed a photo below from ICEMAN6166 in a post he replied to. My question is about how to treat the cowl area to stop the leak. In the photo below you can see where holes rusted through at the forward lip of the bottom of the cowl intake area. In my truck, from the inside, I can see the bottom of this area with a gap and another piece of metal that leads back to the inside firewall. There is some old black material there, either old sealer or the glue to hold up insulation. This material is not consistent all the way across the firewall so there are gaps. I plan to clean it all off, then scrape the little rust scale in a few places and treat that metal with phosphoric acid to stop the rust. My question is: Should I use seam sealer to completely fill this whole void area between the bottom of the cowl and the lip that turns downward to become the inside firewall OR is there another product that would fill this area to waterproof it that I can use? I would estimate it would take a good three full tubes of material as dispensed from a caulking gun. The truck has a decent paint job and I had hoped not to get into full blown metal work(cutting out the cowl from the outside) to address this issue. My thought is that if I can stop the rust with the phosphoric acid and then fill that whole area with waterproof material, should the cowl floor develop a larger leak, there would be no where but down the proper cowl drain for the water to go. I welcome all input.

[foodstick]

Ok, first of all that is a bummer of a place to have a problem !

Here are some of my suggestions, I DO NOT CARE about things looking original when I am done so keep that in mind.

When you open the hood you see the small rectangle access piece in the front center of the cowl? Its about 2 inch tall and maybe 3.5 wide? When I built my 64 I took some of those off other trucks and made it so there were three (I believe) of them across the cowl.. that way I could get in there and work. I build rc airplanes, and I hate having no access to internals. So that transfers over to about everything I work on.
I would go right to where the worst damage is inside the cowl, and I would make a big access hatch maybe 3 inch tall and a foot wide so I could get in there..

Take your time, draw it out and cut it with a Dremel cut off wheel and or 4 inch angle cutter ..spend 20 -30 bucks on cut off wheels if you have to,and do it nice. If you pay attention to how things fit the access will be hidden when the hood is down, and not interfere with the hood when closed either.

Smooth and round the access hole so you can make a nice cover for it out of aluminum or steel.. It could be bolted or riveted on, I would never weld it up..

Clean it up as good as you can with wire brushes.. maybe even a small hand held sandblaster?

Now once you have that hole open you can decide how to fix it, Welding in steel might not be an option, but how are you at glassing?, maybe smearing a real good sealant around in there? I have used a two part epoxy putty that might be the ticket ..form-able with the fingers,hard as rock and grabs well to cleaned metal. You could always paint ,coat ,seal over that as well...

[foodstick]

Another thought, make one big center access hole....you could make a tray that fits up through the access hole, and fits tightly under the openings on top of the cowl, this tray, could have one or two hoses that run down to the bottom of the door post.. that way eliminating water in the actual plenum chamber at all.

[Leeroy]

It's a bugger of a spot, previous slick had this right in the curve behind and up on top of the column near the pedal support. It too had some sort of filler in there that I resealed and left alone but there was flaky rust.

I had the same problem on the mustang with the dreaded cowl vent and repaired it as you suggested. It did work, but realistically it only bought time. When it started to leak again the rust had just spread bigger than the filler, even after treating. I guess if you por'd it, you may have more success but I know that product hasn't always had the best reputation on the forum. I fixed the mustang by cutting out the offending area completely, removing all the rust, treating and putting in a fresh cowl. (Plastic, with sealant this time) 5 years now, it's still good.

Good luck with it.

[bruceandersson]

Another way would be to drill out the dozens of spot welds and remove the cowl vent section so you could really access everything. This would be a lot of work. What about getting the material they make magnetic signs out of and just covering your vents when you are not using the truck? This would not help when driving in rain.

[orangeRcode]

You've got your work cut out for you. Good luck. The good thing is there are several guys who have been in your position and are willing to help!

[Michelle]

Another way would be to drill out the dozens of spot welds and remove the cowl vent section so you could really access everything. This would be a lot of work. What about getting the material they make magnetic signs out of and just covering your vents when you are not using the truck? This would not help when driving in rain.

I had a leak in my 64 Sprint in the cowl vent and took an old magnetic sign cut it to fit and laid it over the cowl vent. I used it when I was away from home with no garage. I have also driven the car with it on and it didn't blow off. I got caught in a hard rain going to LaGrange one day and stopped and got the magnetic strips from the trunk and installed them and drove on to Lagrange. I kept it under sixty and at that speed I had no problem keeping them on the car. I had then in two pieces one for each side of the cowl vent.

[9Fingers]

Thanks to everyone for methods to fix this. I was able to look down through the cowl vent tonight with a small flashlight. I can see very light surface rust inside and a very small amount of dust/debris right along the front edge/seam.

I like the idea of making an access port. I may use a large hole saw from the inside behind the dash, this will give me access and I can either make a removable access plate or i could mig weld it back in. In both cases I'd hopefully be able to save the paint on the front side. I also like the idea of the magnetic material to block the vent.

After I get the front end removed and the engine pulled out I will move it outside and test it with the water hose to narrow down where the leak is and work from there.

Thanks again to everyone.

[Leeroy]

A temporary option maybe? It's for a mustang but would probably work with the minor mods.