Cowl Trough Corrosion

Working on an 86 F350 single cab with a lot of water intrusion. The cowl trough has severe corrosion from one end to another. In one area the gap is about 1-inch, but most is about 1/4-inch gap. Photo shows the worst spot almost directly on top of the gas pedal.



I understand seam sealer is used along this seam, but given that a lot of the metal is gone, Im trying to figure how to work around this. Use a high-solids seam sealer on the smaller gaps? Still wondering how to tackle the large gaps...  

 

Seam sealer will not work on what you have going on there.
You need to cut out the rusted parts and either weld or glue (panel bond) new metal in place to fill the gaps.

Once the new metal is in place you then use the seam sealer to seal the seams so water cannot get between the 2 parts of metal and do this all over again.

With the dash & wiring out you should have room to work from inside the cab to fix this.
You can even do the seam sealer on the inside easy but its the out side that is going to be the hard part as you can only fit your hand / arm in so far thru the cowl openings.
Some guys have that have only little pin holes after a good cleaning have use that spray sealer they show on TV. You know where they cut the bottom of the boat out and put in a door and spray it to seal it.
I think they make a mat type sealer too so maybe after the clean up that may work but you really need to fill the gaps before you go sealing that area.
Dave ----

Thanks Dave. I'll post the progress.

There is a lot of good photos on this over on FTE where a guy cut his all out and fabricated a seamless trough. To do it the 'right' way, yours needs cut out and replaced. Means pulling either the dash or the motor to really get at it. If this is just a use-it-up truck I would clean it real good, get some rust converter (few to choose from) and spray or brush it on as best you can. Then, like Dave also said, get some of the flex seal tape and tape over the holes. I would just run the tape along the whole trough. After that spray it liberally with the aerosol flex seal. It would last for a long time. Just depends upon your plans with the truck and what approach you want to take.

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No brush on, sealer, JB weld type stuff is going to fix that. It's gone. I'm sure if you really wanted to hack it you could get it to stop leaking, but it's going to be a bandaid and make it worse when it really gets bad. Do the sheet metal now while you are in there, or you going to be putting a cab on it because it'll rot the floors out.

ramses wrote

I understand seam sealer is used along this seam, but given that a lot of the metal is gone, Im trying to figure how to work around this. Use a high-solids seam sealer on the smaller gaps? Still wondering how to tackle the large gaps...

See what you have left once you get all the caulk and rust scraped out of there.

If it's not too structurally deficient I'd be tempted to forget the rust converter and go with epoxy and fiberglass.
But then, I'm an epoxy geek, and see using it many places.
It's not as if it's a fender where the back side is seeing the water and mud thrown up off the road.

You'd need to scour the glue into clean metal for a structural bond, and then working while it's just setting up, bridge the gap with some roving and probably lay some light cloth across the whole floor of the cowl from one side to the other.
You'd end up with a continuous composite trough.
It would never rust out if water can't get under any edges, that's why it's important to have it clean and scrub the epoxy into the entire surface before adding any reinforcement.

Being in Puerto Rico you might find someone in a marina or boatyard to help you.
There is fiberglass 'tape' in various widths.
And it definitely needs to be epoxy not polyester.

Jim - so even if the rust is still there (unconverted) the epoxy will stop it from spreading?

I would think the thinking is if you seal the rust from air & water, 2 things needed for rust to grow, it would stop it.
Dave ----

That makes sense. Would the aerosol rubber/bedliner not do the same? Curious since I've never worked with epoxy/fiberglass.

Scott, I usually use West System 105/205,206 resin and hardener for something like this.

You need to get it clean, but the epoxy is fairly thin, so it will wick into cracks and pinch welds if you give it an opportunity.

By scouring while wet you abrade oxides and contamination away, and there's no air that can get back to the surface.

Once this coat is half cured (rubbery, or leathery) you can bridge/fill any gaps, and then lay down some light cloth or tape.
You are assured a molecular bond and the reinforcement will keep the epoxy from being able to crack or tear.
It shouldn't lift, because you scoured it in to the surface.
Covering the whole area means even if water does pool, it can't get through.

Epoxy is a glue first and foremost, unlike polyester.
The West System resin/hardeners are formulated for a certain amount of flex.

I don't really know enough about the chemistry of FlexSeal or the urethane bedliners to say how long they would hold up.
I do know that the Rustoleum leak stop didn't do anything for my floor except keep the water in, and give rust a place to hide.

Hi guys. Went with epoxy and worked out great. After removing the dash had good access. Scraped all rust off as best I could and applied rust converter to all the edges. Then used gorilla tape on inside so epoxy wouldn't just fall in.


Then mixed several batches and applied through cowl openings. Not sexy but its working.


Then removed tape inside.


The I mixed couple more batches and applied on the inside too to "grab" edges on both sides.

I'll be reinstalling wiper motor next but noticed I'm missing the motor's cover that goes under the cowl cover. Only found one on ebay that fits 87's and up. Wondering if it fits too or if I can make it fit with modifications. Dont know part number for this cover. Any suggestions would be helpful.

Thanks again

Well, that should do it!
What did you end up using for reinforcement?
I hope body flex doesn't tear it loose, since you haven't built a 'shell' in the whole cowl.

I don't think much changed about the dimensions of the wiper motor.
1987 went to a two plug system that provided better grounds.

You can compare both motors if you look them up on eBay, or your favorite auto parts chain site.

Just reviewed the whole thread.  Man, that was a lot of rot!  But what you've done looks good.  

On the wiper, I'm not sure I understand what the "cover" is.  I don't see anything in the illustration below that jogs my memory.  What am I missing?

Yes, nice work!

Gary, I believe he is talking about this piece:

Ahhhh!  You are probably right, Scott.

Yes, that's the one. It was missing when I took the cowl cover off. There was a lot of sealant over the old wiper motor so my guess is the previous owner(s) were getting a lot of water on the plug.

Any way been looking but have only found one for 87's forward. Worst case I can make one if I can get dimensions.

I found the one online and it does have a notched area that the 80-86 ones don't but I can't think of any reason why it wouldn't fit. If you want one from an 86  you can have the one pictured for shipping.

Edit: just saw your location. Never shipped there so no idea on the process or cost but happy to help.

Awesome, thanks. How do we get it done?

There s nothing special about that aluminum cover.
You could use the corner of a cut open oil jug or similar piece of plastic to fend off rain, and it would be easy to trim with scissors.