Hello Fellas,

I welded in a patch panel into my lower cowl.
The patch is located behind the lower fender driver side where the bottom trim is located. This is the area closest to the door. I can't find a description what this area is called but I hope I explained it well enough.
I am planning to seal the area with some POR patch but I am wondering if this area should have some drainage holes. It originally rotted out down there and I have had to repair te fender in that area as well.

Thanks in advance,

Sounds like it rotted out from lack of drainage holes...............I'd put some in.

Lets talk nomenclature first.
The area you describe is usually called the cowl side panel. Directly behind it is the outer hinge pillar (that has the holes for the door hinges). The outer rocker panel extends approximatly to the point where these panels join. The small vertical front panel that attaches to the cowl side panel, can be called the outer cowl extension panel, or firewall extension panel. Then you have the firewall (also called the toe panel) The area where the wiper transmissions, wiper motor and upper heater box are located is normally called the cowl top panel(or upper cowl panel). The heater fan blower and housing extend into the upper area of the outer cowl extension panel.
All this being said, the area you repaired is probably the lower cowl side panel and the lower outer extension panel.
As you have guessed, it is designed to drain. The water that comes in through the fresh air opening gravitates to this area, and the rocker panel. This area commonly became plugged with leaves and dirt, never drying out, thus your problem. Also very little attention was given to corrosion protection. Often times, many interior areas were bare, untreated metal from day one. On most models there was not a large drain hole. For a drain, they left an expanded area between the pinch (spot) welds that held everything together. The water was also supposed to flush through the rocker panel and drain out.
If you can, compare the two sides, if one was fairly intact maybe that will assist you in the drain design.
The lower fenders failed for several reasons: bare untreated metal between fender reinforcement and outer skin, inner of fender primed only (lacquer primer), debris build up, (causing moisture retention in lower fender area), and in many areas of country, road salt.
You have the right idea. Be sure to apply corrosion protection to interior of areas repaired, keep free of debris, make sure you have drainage, and you should be fine.
Karl

Wow Karl! I never knew those names but you're right on.
The lower cowl drained into the rocker panel. Water would flow the length of the rocker to the drain at the rear. So when some debris would get through the small hole into the rocker it would sit there and then rust out the rockers. That's why you can get dead leaves out the rocker drains. So the whole drainage thing with the rockers and lower cowls is interrelated.

Thank you everyone especially Karl for the excellent answers,

I assumed the same thing about blockage in the lower cowl side panel due to leafs etc. When I first started taking it apart there was a large amount of debris in that area. I assume GM engineers never accounted for the debris clogging up the drainage area found bewteen the spot welds. The other factors mentioned played a role in the rust damage as well.

Unfortunenately I don't have a good sample on the other side to compare to but I have a general idea of how it could work. The next thing to do is to POR-15 the inside of the patch,cut a end piece and weld it in, POR patch to seal it up, and then drill drainage holes. The size of the holes I am not sure of or whether it is better to have 1 big hole or many small holes.

Thanks again,

Kris