I have an 86'F-150, today I pulled out the heater box and noticed some thick scaly rust at the seem on the firewall. This is the seem underneath the windshield wiper compartment. I could see some rust from in the engine bay and I was concerned, but now I realize it's worse than I thought seeing it from the inside. I need to stop this rust. Tomorrow I'm going to wire wheel the area to see the damage. I'm assuming there must be sealant at the bottom of the windshield wiper compartment, and I plan to get in there and dig out the old stuff and reseal it. So all I need is a thin rust killer to poor into the seam to kill the rust. Anyone have a suggestion for a product?

 

For the rust killer, por15 or Eastwood encapsulator are the two best. I prefer Eastwood as it's a little more uh, forgiving I guess is the word. But por15 is sure impressive once dried. Both are pretty watery so will flow down well.

As for the whole issue in the cowl area, do a search on this forum as there are at least two good threads dealing with it.

The body shop doing the work on my truck had to cut out the seam from the engine side and repair it that way. Once that rust gets down in the cracks, it's tough to stop.

I did some cleanup on mine before I dropped it off at the shop and found that a Dremel with the flexible extension and a gob of wire wheels did a nice job getting in there.

 

Well I hope I don't have to cut it out to fix it, not sure if I want to spend that time on it this year. Thanks for the info on the POR 15. I was hoping to hear it was watery.

 

I think I'll scrape out the old crap,clean it as good as I can, then use baking soda and distilled water on it for a few days. See if I can get that rust to turn black, then maybe use the POR 15. I don't wan the rust to spread anymore.

 

I've never done the baking soda option but you may want to call por15 support to ensure it won't interfere or someone here may know. Por15 is designed to go directly on rust (after loose is scraped off) so I don't know if I'd bother with any other method.

 

POR 15 also has a "Metal Prep" (acid) they recommend using before painting.

 

I need to go do some organizing and see what parts I can put back on the truck because I have a pile of stuff laying around. Maybe later tonight I can clean out the cowl and wire wheel the firewall to see the damage. I've been looking all over and the most promising thing I've saw is rust dissolver, but it looks like a messy process and would probably lead to a lot of repainting areas that are still looking fine. I'm skeptical about being able to just put POR 15 in the crack without first neutralizing or removing the rust somehow. Rust is a stubborn thing. I've saw threads on here of people using rubberized coating but I don't recommend it at all. I did that to the floor pan of my old Dodge, and all it did was encapsulate the rust. The rust continued to spread, but worse, the rubberized coating is horribly stubborn to remove. It has a tar like base to it which cannot be cleaned other than chemically. Wire wheel it and it heats up like grease and just spreads around. Also, if the rust is pitted at all, the stubborn crap fills the small voids making it impossibly to wipe off, so it ends up needing a chemical bath, and I mean totally submerged bath which isn't feasible at all. I don't believe the Baking Soda is going to be good enough to dissolve rust either now that I think about it. Anyway, I have some head scratching to do.

 

As mentioned: POR15 Metal Prep

Also KBS coatings has a rust paint and a metal prep also.
Phosphoric acid is also a good metal prep

 

I was just out there eye balling things and I think I'm going to remove the engine side cowl piece and clean the seem properly. I noticed there is sealant filling the seam that will be impossible to remove. I'm not confident that I will be able to kill the rust without it starting back up again no matter what I use. I'm also pondering a way I can weld it back together without having a seem at all in the end. I don't want two pieces sandwiched together for rust to collect. I think it will be time consuming but better in the end. I will start a new thread when complete to show what I end up doing.

 

I used the acid to kill rust on panels that the Eastwood encapsulate would not be a good fit for.
Por15 & the Eastwood seal the rust from air & water so it will not rust any more.

Under coating does not seal rust and the coating has pin holes and water & air can get thru and keep rusting as you found out.
Dave ----

 

So do you think the phosphoric acid would get into it and dissolve the rust? How is it with surrounding paint? Also, because there is sealant sandwiched into the seem as well, would the acid melt it out too? I don't want to touch it again for another 30 years, is all I'm saying.

 

I would clean out any dirt, rust and old sealer you can get at.
Then spray the acid on the rust areas. I let it sit a day or more till I can get back to it then wipe it down with a damp (water) sponge rinsing it and let it dry for a day or 2.
I would then replace the seam sealer, they make it in a tube for caulk gun or brush able. The us is nice if you can
get it in the area to force the sealer in the gap. The brush type, I used SEM gray in color, works nice. I work use a small acid brush to get is where you need it.

I have also seen it posted of guys using the spray sealer seen on TV to seal the bottom of a boat. Take one of them straws that comes with carb cleaner to point the sealer where it needs to be.
Once the sealer is dry I would use that straw thing and spray paint the area.
Dave ----

 

That sounds like just the stuff I've been looking for. I think I'll wire wheel all I can, then gorilla tape the bottom of the seems then fill it up with that stuff. I still have a tube of seem sealer I used on the drip rails. I'll post pics tomorrow.

 

Before you put the tape on treat the rust with the acid till it turns the rust black and is dry then wipe down with that damp sponge, when dry then use the tape.
I think I might even use the sealer, the TV spray or seam sealer or what you have, before the tape and then tape and maybe more sealer?
When I do any thing like this it is all seat of the pants but I want what ever kills the rust to go on first and why the acid before anything else.

I was lucky inside the cowl area was in pretty good shape and most of the cracked seam sealer was on the outside and easy to fix.

Once I removed the old cracked body filler from the cab of my truck there was rust. I treated this with the acid before I did any body work to it other than pulling any dents out.
My tail gate when looking at it had rust under the paint so I had to strip it down to bare metal and treat it with acid or it would have come back thru.
The reason the filler cracked was from the rust and it was way to thick, I should not have any issues with that now.
Dave ----

 

Just a tip on using acid, make sure you're wearing a respirator at the very least.
The vapors will burn your sinus's/lungs.
I like using acid, it's cheap and works very well. But precautions need to be taken.