Can someone explain these to me the whole theory Behind them ? There floor drains so to speak to keep the car from filling up with water ?? So why does everyone seal them in making them useless I would think. Or is it a pressure thing once submerged they are supposed to pop. I've seen them patch paneled over, screwed down, seam sealed, caulked, body filler over top you name it. So what's the point of having them if there getting sealed in. People are so concerned about rust and water getting in, they seal them up tight which renders them useless ??
Or am I way off base and they were only used for dipping bodies at the factory after that do what you want with them, GM sealed them up ?? Also real quick while I got you on the phone, cups up or down and what's that theory as well. Sorry I don't have time to dig for this answer as Im sure it's been discussed.

 

Think they dipped the shell in primer or other chemicals to clean on the line? On my 72, there are factory paint runs on the bottom of the floor pans that run front to back.....

Probably had more to do with production/manufacture than for use after delivered.

 

I would bet on that being correct. About like freeze plugs. They will not keep a block from cracking. I believe they are there to get all the sand out during manufacturing.

 

You want them holes sealed for sure. No avenue for exhaust, moisture, critters, or other nasties to get in.

Cup up or down- I want to know also. I will look next time I get to the parts cars.

 

Cups up from everything I'm reading. However it was never an issue when they went in the wrong way on the line. Cups up is to keep from pooling at the drain plug.

 

I see most of them with the cup up but I have seen some with the cup down.

 

I think they were put there by the manufacture for people to get rid of there stash quickly in a inconspicuous way if they were pulled over by the cops.

 

The holes are there for mainly one purpose, although there is a secondary purpose.

As many have surmised, the main reason is to allow a chemical to drain. I am sure that GM used a rust preventative to keep car bodies from rusting that was a dip. Nowadays, we use an electrolytic discharge method to attach it to the car body. Sheet steel comes in rolls and is often treated for rust prevention, but, once you cut and stamp it, you have exposed edges. Welding then further burns it off.

You take the completed shell body from weld, and you have a dip pool just like a log flume ride that takes the car through it. It drains into a catch area through all those little holes. It dries or flashes off, sometimes washed off, then the traditional paint process begins.

Currently, we use black plastic round stickers that we call hole plugs to block everything. Gives the car a 5 year or so delay on corrosion starting there.

The second reason is an access hole. If you need to bolt something together but can't access it, often there will be a coaxial hole to do it through, then you plug it once done.

They should all be plugged, unless you have a leak someplace and just want it to drain.

 

This is exactly correct. The entire welded body shell was dipped in a primer bath. The plugs are solely to allow the coating to drain out. I toured the Framingham plant in the late-70s and watched Cutlass and Regal body shells doing exactly this. The photo obviously isn't that vintage, but you get the idea.