Firewall water seepage

[toddcripe]

Continuing to try to track down why I'm getting water in passenger floor on my 1999 Prerunner when it rains hard, I'm about 10 hours into trying to figure it out and am not any closer now than when I started. Anyone have issues with water getting in around the seals on these two things that go through firewall on passenger side in photo below? I'm assuming one is the windshield wiper motor and the other goes to HVAC. They are not watertight.

I've checked A/C water drain and it's not clogged, so pretty sure it isn't that. Took fender off today and nothing looks out of place and the cowl drains water, so its not clogged up there.

My latest theory is that water is running down the firewall and getting into the cab that way. The cowl design on passenger side is different than driver side. On driver side it comes off windshield and is able to go through the cowl trim cover and drains right out. The passenger side doesn't allow the water to travel the same way because the whole passenger side is one sealed unit, which I presume is to protect the windshield wiper mechanism. The problem with that is heavy rain causes water to go down the firewall. Pretty sure that's where the water is coming from that's on my passenger floor.

I'm trying to avoid taking the whole dash off in order to seal the firewall from the cab interior. That seems like it would be a pain in the a$$. Any other thoughts on someplace else that needs to sealed? Would take some pretty small hands to get inside the cowl space on passenger side, so if it's that I'm screwed. Appreciate any help. Thanks!

 

[tacojoel]

Some toyotas around that age had these small white plastic grommets outside under the wiper cowl that disintegrate over time causing water to leak by the firewall to the inside passenger side under the glove box. Using rtv sealant to cover those grommets will stop the leaks.

 

[JayQQ97]

i remember a pic from that other taco rag long ago where someone had this similar issue and actually cut into the sheet metal on the fireWall by the wiper motor and peeled it back for access

 

[tacojoel]

My tundra had bolts, or screws on the wiper cowl that fastened it to the firewall. Was kind of a pita pulling the wiper arms off to remove this cowl, but was worth it, when I found the source of this leak every time it rained.

 

[JayQQ97]

toddcripe, have you ruled out the windshield seal area?

Anyone cut through cowl? Pool in passenger floorboard

anyone cut through cowl above fresh air intake? I have caulked every crack and hole around area of pass. side cowl 03 taco

www.tacomaworld.com

 

[JayQQ97]

another post from crustyTaco at that other rag
i respect that guy from Louisville, very few respectable chumps at that rag... very few

The infamous passenger side leak.

Just confirmed Ive got this leak in my 02. Is there any consensus over whether to use a spray sealant (like in the TSB) vs caulk? Is there any reason...

www.tacomaworld.com

 

[toddcripe]

Some toyotas around that age had these small white plastic grommets outside under the wiper cowl that disintegrate over time causing water to leak by the firewall to the inside passenger side under the glove box. Using rtv sealant to cover those grommets will stop the leaks.

Yes, checked that and they are in fine shape. Most of this truck is in excellent condition, previous owner took great care of her.

 

[toddcripe]

toddcripe, have you ruled out the windshield seal area?

Anyone cut through cowl? Pool in passenger floorboard

anyone cut through cowl above fresh air intake? I have caulked every crack and hole around area of pass. side cowl 03 taco

www.tacomaworld.com

yes, good suggestion but I took off all trim and hit it with water pretty hard and no leaks around windshield.

 

[toddcripe]

i remember a pic from that other taco rag long ago where someone had this similar issue and actually cut into the sheet metal on the fireWall by the wiper motor and peeled it back for access

If the sealing I do today doesn't fix the issue, I'm considering cutting a replaceable top out of the passenger cowl over the windshield wiper mechanics so i can see what's going on in there.

 

[toddcripe]

My tundra had bolts, or screws on the wiper cowl that fastened it to the firewall. Was kind of a pita pulling the wiper arms off to remove this cowl, but was worth it, when I found the source of this leak every time it rained.

TJ, I'm hoping to avoid doing that, going to seal everything else I can easily reach first, but if I still have the issue there's only one place left to look and that's in that enclosed area you can't see or access.

 

[toddcripe]

another post from crustyTaco at that other rag
i respect that guy from Louisville, very few respectable blokes at that rag... very few

View attachment 43812

The infamous passenger side leak.

Just confirmed Ive got this leak in my 02. Is there any consensus over whether to use a spray sealant (like in the TSB) vs caulk? Is there any reason...

www.tacomaworld.com

Good string, thanks for sharing. I saw the factory update from back in the day that essentially said to seal everything you can see, so that's what I'm doing this afternoon including the pinch weld that goes the width of the cab and anything else that is remotely close to the passenger side firewall.

 

[tacojoel]

Good string, thanks for sharing. I saw the factory update from back in the day that essentially said to seal everything you can see, so that's what I'm doing this afternoon including the pinch weld that goes the width of the cab and anything else that is remotely close to the passenger side firewall.

I did all that crap to on my gen1 tundra, but in the end it was under the wiper shroud...royal pita to remove that shield for these 3 white grommets. Hopefully you need not have to go in there for a tacoma.

 

[toddcripe]

Today's update. I've cleaned everything up so am waiting for all surfaces to dry so I can hit them with seam sealer on the metal seams and silicon around the one suspect rubber grommet where the wire bundle goes through the firewall below the cowl bottom.. I'm amazed how good of condition this truck is in. There's not a speck of rust anywhere that I can see on the firewall. You can see for yourself in photo below how clean the firewall is after I took the wiper motor and heater covers off. There's no reason to put additional sealant around the wiper motor grommet because it is above the cowl bottom and doesn't have a direct path into the cab.

When you look inside the cowl where the wiper mechanics are, you can see from second photo that it looks like it just rolled off the factory floor. Took off glove box and hvac ducting and the parts of the firewall I can on the inside are perfect, so I'm not going to take anything else apart inside the cab.

I put a super bright light in cab pointed at the passenger firewall. No light comes through anywhere, so no obvious place for water to get in. Regardless I'm putting seam sealer on every seam that is below the cowl bottom. The one that forms the side of lower passenger compartment and continues across the floor is a suspect because it doesn't have visible caulk coming out of it.

If that doesn't do it I'm cutting an access panel in the top of the cowl on the passenger side. I've got about 15 hours into this so far and I'm no further along than I was when I started.