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Discussion Starter #1
Does anyone have pictures of where the cowl/firewall leaks on the passenger side? I just fixed my clogged ac drain hose and left the carpet pulled back and can see water coming in along the firewall. Insulation on floor and up under the heater box is soaked.

It seems I need to pull the wheel well off to access the box, but what else do I need to do to access where I’m assuming some seam sealer has failed? I’ve searched fo hours and not finding what I need.
 

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Did you check the bottom cover of your evaporator pan and also that the evap drain elbow is connected? I thought i had a cowl leak too. Blew it all out, cleaned everything, ensured the evap drain elbow was there. Still had a wet floor on the pass side. Pulled off the pan for the evap/heater core and re sealed it. No more water.
 

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Yeah the 16” hose I have on the drain elbow actually was clogged with mud 4 days ago and leaking. Cleaned it out and all was good. It rained hard yesterday and today and with the carpet out, I can see a slow stream of drips coming in.

Your leak was the bottom plastic cover that sits behind the glove box area? I don’t see it leaking anywhere and I’m looking at it with the glove box removed, but it could be from the area against the firewall.
 

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Mine had a crack beside the outlet. I heat welded it, and was exceptionally careful when reinstalling it. I keep a couple of spares just in case I have to pull it again. It took me 4 years to figure it out.

The long hose is overkill, and will get clogged easily. You should shorten it, or keep the end above the frame rail.
 

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There is a thread on this forum concerning rain leaks due to the factory seal sealer failure, in the cowl.
 

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Well I dropped the pan and not sure if it was leaking from there. Now I know this pan was overflowing on Monday due to a clogged drain hose and there is a 1” hairline crack towards the bottom left screw hole in the pic. It is along the rearmost part of the pan at its highest point and was not leaking today as I sat in the car watching water come from the drip elbow area of the firewall. It never leaked a drop onto the floor last summer with the ac on and the original seal that was re-used when I replaced the heater core a few years ago.as shown.


 

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Discussion Starter #7
There is a thread on this forum concerning rain leaks due to the factory seal sealer failure, in the cowl.
I found a few topics like that without pics but am looking for a visual before I get into a half day project. I know I will end up breaking some wheel well bolts as well due to corrosion and never having been removed.
 

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Mine had a crack at the white circle. You stated that yours has a hairline crack at the red circle.

I used silicone sealer to make a new gasket, and that may help.
 

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The crack is actually the opposite side from the red circle. So, towards the rear of the car when installed and the highest point of the pan. I just plastic welded it shut on both sides and will reseal with silicone in the morning, allow it to get tacky, and loosely install the screws to let a seal form in the channel. It definitely was not leaking from there yesterday or today when it was raining. While that’s drying, I’ll cut the hose back to right under the top of the frame rail and take the cowl panel off to clean it out. Sunday I’ll see if I still have a leak and if so, use seam sealer on the areas on the firewall that fail.
 

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Discussion Starter #10
Well the heater box is sealed and wasn’t the issue. I removed the cowl and it was very clean underneath. I only wiped down with a wet rag before taking this pic. The seam sealer has cracks in it so I’m planning to skim over it with seam sealer rather than attempt to remove it all since it’s pretty hard and in there really good. Would this likely be the cause of the leak?


 

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You must find the highest point that the water enters through. My car had the windshield leak along the bottom where the urethane separated from the body because of rust. The only way you can really check this is by removing the glass. You could also remove the dash, including the support.
 

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Discussion Starter #12
I ran a hose for 20 minutes over the cowl area pictured, right below the opening for fresh air and no leaks. So that’s not the area leaking either.
 

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In my case, a water leak after opening the HVAC box and replacing the evaporator was due to the foam seal that goes around the AC pipes where they exit the plastic box. Dumb design, easy to overlook, and hard to get it properly installed.



It squishes up in there, fits around both pipes. If it's not well-sealed against the pipes AND the box, water can drain out of the gap between the AC pipe and the box.



Drove me crazy trying to sort it out, especially since I could see the box seam was tight and the drain tube was sealed to the drain fitting and draining well. On a warm humid day the system makes a lot of water, and putting the AC evap pipes opening near the bottom of the drain wasn't such a brilliant idea on GM's part. That foam seal was a quick-fix that has to do triple-duty: seal the firewall openings, absorb any misc condensation from an inch of the cold AC evap inlet pipe, AND seal against dribbles or sloshing from the plastic box at the pipe openings.



Drying out the carpet and underlayment was fun, too.
 
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