APB - Check your cowl seam seals!

[da_raabi]

Fellow Square Owners:

If you have the time I would recommend that you pull the cowl cover off your truck and inspect the bottom of the plenum. GM in their infinite wisdom chose to join the inner and outer firewall sheetmetal as a seam at the bottom of the cowl plenum - you know, the place where ALL the rain goes off the hood/windshield.

GM used seam sealer on this area but with time the sealer dries out, cracks, and begins to let water into the seam between the two sheets of metal.

About 2 years ago I first realized this was happening when I started getting a leak in the cab. Water was actually coming in through the various bolt/screw holes in the firewall. It took a bit but I quickly realized it was actually seeping from between the sheetmetal pieces. Woah.

I pulled off the cowl cover and discovered the issue. So I cleaned up the area and put new seam sealer on. Note I did NOT POR-15 or chip out all of the old sealer.

Now I am paying the price.

We have had heavy rain for the past couple of weeks and a couple days ago when it stopped I decided to go out and vacuum the truck. Well that was when I discovered that the floor was SOAKED.

I checked around and found basically the same problem. So off came the cowl cover again and... oh my. Apparently rust had continued to grow under the seam sealer (new and old) and had started forming holes and leaks. That was where the rain was coming in.

So now I have chisled out ALL of the old stuff, wire wheeled what is left and now I need to fill all of the holes, POR-15, seam seal, and then I plan to use flex seal or something to completely cover the entire cowl area so that water will NEVER hit that seam again. I had standing water between insulation layers under the carpet. It was nasty. NEVER again!

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[Vbb199]

I was wondering why my old 90 burbs floor was constantly wet, despite changing the heater core AFTER it blew up.


Makes sense now.

 

[80BrownK10]

I was wondering why my old 90 burbs floor was constantly wet, despite changing the heater core AFTER it blew up.


Makes sense now.

Yep this spot leaks on them all I think. This is what rusted out my trucks floor and got the edges by the rockers and floor pan. I just put silicone first. It lasted 8 years maybe and pulled away. This time I cleaned all the loose old out and wore wheeled it. Used rust converter on it and let it run down between the seam best I could. Used GM seam sealer on it and then painted it all with Rust-Oleum paint.

 

[80BrownK10]

The whole idea , I agree was stupid. That area should have a weld running there if it was where tow pieces were to meet. And over that weld have some amazing paint and prep, because all the water and crap that goes through there. Especially since trash will collect in there and sit moist causing potential issues.

 

[Octane]

My 1977 leaks somewhere there and it drips down past the vent door down to the floor.I find the windshield is not leaking tho

 

[da_raabi]

Only my square has this issue. I've never seen it on any other vehicle. My 80 Camaro uses a solid piece of metal there with no seams. That would make sense right?

Keep in mind that area of these trucks was probably designed in the 1960s and held over ever since. Trucks in those days were designed to be run into the ground in 5 years or less. I guess they figured it would never be a problem in that amount of time.

Just do yourselves a favor and do what I and 80BrownK10 have done.

 

[RecklessWOT]

huh. Yeah the carpet in my burb is always wet too. I always assumed it was coming through the windshield seal, but after having the windshield and seal replaced a couple years ago it's still the same. I'll have to check out that area when I tear the whole truck apart this fall

 

[shiftpro]

Only my square has this issue. I've never seen it on any other vehicle. My 80 Camaro uses a solid piece of metal there with no seams. That would make sense right?

Keep in mind that area of these trucks was probably designed in the 1960s and held over ever since. Trucks in those days were designed to be run into the ground in 5 years or less. I guess they figured it would never be a problem in that amount of time.

Just do yourselves a favor and do what I and 80BrownK10 have done.

Yes our 35 yr old trucks are beginning to leak... I call that pretty decent engineering..

Thanks Adam for bringing this up and reminding us all.
The only thing I would have done different, was to use a rust convertor before the POR15

 

[OldBlueDually]

Here is my personal choice for sealing stuff like this up! I have used it in my basement too for sealing up cracks, used it on a rubber fernco clamp to cast iron, painted surfaces, wood, metal....you name it. This stuff is around $10 a tube, but worth every penny!!!

I plan to use this on my 76 GMC, in those places you are speaking of. The flexibility and durability of this stuff after is cures is unreal.

Nice thing about this stuff below, I will use my rust convertor on it, then paint, then use this OSI. Or it could be done right after rust convertor, then paint over it...either way, this stuff isn't going to let anything through!

http://www.ositough.com/en/products/featured-products/quad-max-clear.html

 

[RoryH19]

Good to know.
I'll check my k5 while it's apart for painting.
Thanks.

 

[Madhorn]

Had the same feature on my 77k10. Lots cutting, grinding and welding to fix it.

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[80BrownK10]

Yes our 35 yr old trucks are beginning to leak... I call that pretty decent engineering..

Thanks Adam for bringing this up and reminding us all.
The only thing I would have done different, was to use a rust convertor before the POR15

They usually leak way before the 35 year mark. Usually there rusted totally through by then.

 

[Rusty Nail]

I reference this bookmark all the time. Sad to hear you still fight it Man, thanks for posting.

https://www.gmsquarebody.com/threads/water-on-floor.15825/

 

[olnick]

I found the exact OSI product about 5 years ago! It is the ONLY product that is still in place! I used it to seal the seams on my deck to keep the rain/snow and other water from getting through and soaking my winter wood fuel. Now after 5 years in place I have two small drips that need attention prior to my wood stacking this fall! I give the OSI product 10 stars. The one and only down side is to make sure you use a good VOC painting mask as the fumes are wicked strong/bad!

Olnick

 

[da_raabi]

I reference this bookmark all the time. Sad to hear you still fight it Man, thanks for posting.

https://www.gmsquarebody.com/threads/water-on-floor.15825/

Ha! So you found it! I'm glad to hear my troubles are helping out fellow square owners.

I just finished up the fourth step in the process. So I have:

1. Removed as much of the original seam sealer and rust as possible using a screw driver (seriously) to chisel and scrape it all out, vacuuming the remainder.
2. Liberally sprayed it down with POR-15 Metal Prep. I don't much like this stuff, but as long as you wash it off with water correctly it works well I guess. My hope was that it would get between the sheet metal layers and convert any rust in there.
3. Liberally applied two coats of POR-15. Used about one half of the tiny can of the stuff.
4. Applied 3M seam sealer. I used an entire tube to completely fill the entire crevasse. It's a bit messy but its filled.

Next step is to completely coat the entire plenum with Flex Seal. My hope is that this will prevent water from ever reaching the area again. I'd rather use a big U-shaped piece of aluminum or something across the entire thing, but there would be no way to get it in there, and even if I could it would rattle like crazy. I figure Flex Seal should do the same thing.

Hopefully at long last this will fix my issue. I was pissed when I saw how nasty my brand new carpet, mass-loaded vinyl insulation, closed-cell foam insulation, and foil-backed butyl insulation had gotten. Fortunately it never got to stinking, so I'll take what I can get. The carpet is stained, but only under the floor mat, so I guess its not too too bad.

More to come.