Recently while working on my truck I noticed that there was rust on the floor pans under the passenger side. After all the rain we had in Houston this weekend I discovered that it seems to be caused by water leaking into the cab.

After the rain, I pulled the flooring up again and the padding on the bottom was soaking wet and I noticed moisture all the way up the passenger floor to the back corner of the firewall. I checked the seals on the rain gutters on the roof and those seem to be good.

I was thinking that maybe the water was leaking in through the box where the heater core sits, but I'm unsure if this is actually possible. I want to try to find it's source and seal it. What are some locations in this area where leaks may form and allow water to get in?

 

Good question, is your problem along the strip that holds down your carpet close to the bottom edge door seals ? I too have the problem on both sides and have cut out sections inward of the rocker panels (donor truck) about a foot on both sides to cover my problems. On the passenger side for myself near the rear lower seat belt mounting pont is my problem. Will watch for other responses as to the cause .....

 

Here is the image of the rust problem I have. The water seems to be coming from the back right corner of the firewall on the passenger side, as well as a bit was on the kick panel as well.

 

I just fixed this in August.
You either need to reseal the cowl or look under the cab where the mount is boxed in.
(Pull that rubber plug)

Water always runs over and sits against that pinch weld flange the weatherstrip attaches to because of the pitch of the floor.

Leaks into the A-pillar are a big problem if not addressed asap.

 

There is a drain the in the heater box that tends to get plugged.

make sure it is clean

 

Do you happen to have any tutorial on how to get to this plug?

 

Look under the truck. The bottom of the heater box will be a drain

 

Could you provide some further details on this? Now that I'm almost done fixing my rust issues, I thought it might be a good idea to fix the source.

I also have a leak at the back passenger side somewhere. There was a little splash of water on the upper ledge, sorta behind the passenger's right shoulder on the floor.

 

Remove the wipers and antenna.
Remove the cowl and chisel all the old cracking seam sealant out.
Go to the bottom where the rubber drain is behind the wheel well.
Pull the drains out and use a hose to flush all the muck and chunks of sealant out the bottom.

Take a hook tool and open the seam from the upper windshield corner across the rain gutter and around to the back window.
Use a little wire brush to get back to metal.
Epoxy dtm primer and replace the body caulk.

Buy the better ($20ish) caulk.
It will be cheaper than doing it again.

 

The heater box drain needs to be clear or it will fill with water and dump on the floor.
Not sure if you have water *on the floor* or running down the firewall/kick.

 

Thanks very much for the detailed write-up. I've definitely got some cracking of the sealant in the gutters. That all needs to come out, rust-treated, and re-sealed. Any specific suggestions on the body sealant?

FWIW, I've found Loctite PL S30 Polyurethane Roof and Flashing sealant (Loctite PL S30 Polyurethane Roof & Flashing Sealant from Loctite Adhesives) works very well as a seam sealant on the bottom side and inside the cabin. But I think I'd want something more solid and UV stable on the roof.

 

You don't think s30 or s40 don't see a lot of UV when applied for their intended purpose?
I used Sikaflex on my gutters.

 

Also check out the upper brake light if you have one.

 

True. I just haven't tried painting it. I'm inclined to think the paint would fail sooner rather than later, but I'm just guessing.

Do you happen to remember which Sikaflex? 252 maybe? Did you paint it?

 

Sika NP1 I believe.
I used it because I had some gray left from a storefront.

If I were going to buy something I would just go to the bodyshop supply.