Holy Cowl!

Early Mustangs are notorious for having rust in the cowl area, usually so bad that rain water drips inside the car and rusts out the floor pans. I can't see any evidence of a leak but then again this car probably hasn't seen any rain in many years. It did drizzle a little on my lone trip but not enough to make me roll up the windows. From the outside the center cowl area looks clean with a texture on the bottom which is probably some kind of sealer, but it's impossible to see the sides where the fresh air "hats" are located and where rust usually occurs.

The driver side vent was working very stiffly and looking up under the dash I could see it had some surface rust. I decided to remove the vent and spiff it up while at the same time get access to the bottom of the cowl.

Here's the nasty looking vent. The rust is mainly at the top were it bolts to the cowl, but at least the rubber seal is still pretty pliable.

This is the bottom of the cowl looking up through the hat. Water is supposed to run around the hat and drain down the side of the car behind the fender, while fresh air blows through the hat down into the vent assembly. At first it didn't look too bad for being 50 years old but when I scraped off the flakey rust it got worse.

Using a small mirror I was able to look on the other side of the hat at the horizontal surface of the cowl. It looks like the the rust is limited to the hat as the flat parts look really good. Fortunately this is a common problem and there is a repair kit available.

These replacement hats fit inside the originals and will never leak if sealed correctly. I will NOT be using the silicone sealer that comes with the kit as it contains an acid to help it cure but can be corrosive to steel. I ordered some body sealer to use instead. I debated whether to cut out the old corroded hat or leave it like the kit instructions say. I think I'll cut it out since it's not going to be a benefit to the repair, and more importantly, I'll be able to seal the rest of the cowl area with it out of the way.

Before I started I coated everything with Corroseal Rust Converter just because it's fun watching rust turn black. Then I used a 3" cutoff wheel in my pneumatic die grinder to cut the hat off. I tried to cut as flush as possible without damaging the horizontal flange so as to minimize any lip that could trap water.

Btw, in order to work on this area, I have to lay on my back with my head and right arm under the dash, my feet in the back seat (I had already removed the driver's seat, steering wheel, and pedals). It's extremely awkward just taking these photos let alone actually working on anything.

Three songs later (about 10 minutes) and it was over.

You can see the rot was much worse on the side I couldn't see (it's upside down). I used a mirror to assess any remaining damage.

This is the horizontal surface on one side where water sits and rust-through would have been a serious problem. Not too bad.

Here's a view looking towards the outside opening of the cowl. As you can see there is very little rust. The next step was to clean and prep everything I could reach before treating it with the rust converter. I took my time here as I wanted to get rid of as much rust as possible before coating the surfaces with body sealer. Then I can seal in the new hats.

I dry fit the new hat before sealing it in place. For some reason that one stud was bent so I had to straighten it out.

Here's the fresh air vent after I spruced it up.

And here's the results of all my labor. I know it's not much to look at, but you can see the vent in place. I'll eventually get around to doing the passenger side cowl, but since it requires removal of the heater assembly I'll wait until I install the A/C.