superloaf

Changed my battery the other day and found a hole rusted through the metal underneath. Inside the hole there is a soft fabric like material which feels like a comforter or pillow. Is this some kind of sound dampening material? Never seen anything like this on my car in 20 years so just was curious.

Also, I can't tell if the hole will drain into the interior of the car or into the fender liner--does anyone know? It's pretty close to the engine side of the rain tray so hopefully it's draining to the fender. (It doesn't rain that often here so no sign of front floor drainage....)

I assume that this was solid before the rust? Or was there drainage hole there which just got bigger?

And I know I should patch it somehow but not sure exactly as the battery acid will cause further problems. What would you body work experts suggest?

Many thanks in advance....


Some pics of the offending hole:




Close up of the fabric material:




And then I managed to break off the vacuum hose connector on this reservoir. I assume this is to control the HVAC flaps, correct? What exactly is it called as I'll need a new one:

Tiger03447

Not uncommon to do this to a vacuum reservoir. Go to your local hobby shop and get some small diameter brass tubing and epoxy it into the hole on the reservoir. better than new, or you can find them on e-bay for about 20 bucks. The hole in the battery tray is not the one you want to see. There is a hole in the battery box that leads out to the engine bay, but this isn't it...so do a repair to the hole, and then you can spray it with undercoat after cleaning with bicarb of soda and water and a toothbrush..or maybe someone makes a Stainless steel liner for it, or you can get a plastic marine battery box, cut it down and use the bottom as a tray. AutoZone has them for less than 20.00. You'll have to rig a new hold down for it if you do..Hope this helps some, Tiger 03447

divil

Unfortunately that is definitely draining directly onto your DME. The soft material you felt is the sound deadening right behind the DME bracket,

Take a look at my previous threads on this - it's a pretty big repair job if you want to get rid of the rust completely.

superloaf

Thanks guys for the grim news....Very strange to see since I'm in LA and rain is so minimal. Wish I had caught it sooner.

Guess I'll try to neutralize the acid and then grind and sand it. I also have some stuff I bought for my old Alfa called Corroseal which turns rust to mangenite which can then be painted or patched. Although I did see some problems when using this with zinc coated metal so now not sure what to do. I don't have a welder so if I clean it up and bondo it, will that hold it for a while? I realize that with the acid, it won't be a permanent fix until it is replaced with fresh steel but that is beyond my funds and/or expertise at this point.

Are there any other options I'm not aware of? I need to get this patched before the DME & KLR get messed up and of course it's supposed to rain tomorrow....

plumbum

My old 951 had a similar hole...I found as a cleaned the area many more small holes. Once you get it fixed get a factory battery cover, it's my understanding that that is one of the reasons they rust under the tray.

Jerry Feather

The area of this series of cars where the battery lives, along with the interior fan assembly and the SW wiper assembly, and fuses in the later cars, is called the Cowl area. The bottom of it is the top of the footwell inside the passenger compartment. The front of is it the top of the firewall. Along the top of the front edge is a rubber bulb seal that is intended to keep air from the engine bay out of the cabin, and perhaps to keep water out of the engine bay somewhat. That seal mates with the underside of the hood when it is closed.

The Cowl Area is the place where almost all of the water off the WS and off the top of the hood is supposed to go when there is precipitation. The WS wipers swipe the water to the bottom of the WS and it drains into the Cowl area. In there it runs along the bottom of the Cowl area toward the front at near each end to a drain hole on each side where it drains forward through the firewall and down onto the ground.

The rusted hole in the OP's Cowl floor appears just aft of and below the passenger side drain hole. That should be the low point in the cowl floor on that side of the car. Nothing can be done about having water in the cowl area because there is no where else for it to go. A battery cover will do nothing to keep water from off the bottom of the cowl area. Even the plastic Cowl covers devised by Porsche for the later of this series of cars does nothing to prevent water from getting in here, it only helps direct it away from the fan and WS wiper mechanism.

Even the more nearly full Cowl Covers that I am developing to cover most of this Cowl area on, perhaps, all of these cars, will do nothing to keep water out of the cowl area.

So, what I suggest that Superloaf do is to temporarily plug the rusted hole, so that sand does not fill the cabin, and have the rusted area sandblasted to get rid of the rust, then perhaps trim the hole a bit. Then I would cut a patch of steel to the exact fit of the area rusted and cleaned making sure that the two surfaces match pretty closely and without raising that surface much or any, since it still needs to be a low spot in the Cowl floor. Then I would epoxy prime both the sandblasted area and the patch. Then I would simply glue the patch in with body panel adhesive that is probably two-part from the auto body paint store. Then finish the repair with a thin coat of undercoat, probably from the same source. Be sure that the drain hole in the firewall just above the repair is open to the very bottom of the Cowl floor.

After that you must be more careful to clean debri out of the Cowl area that tends to accumulate and that will plug up the drain holes allowing water to accumulate in there and rust the floor.

plumbum

My understanding is the battery cover prevents water running over the battery terminals which can lead to corrosion.

divil

It might also keep leaves and things like that out, which tend to block the drain channel.

It's a good idea to unblock and test the drain channel regularly. Whenever you was the car you should see water spilling out the bottom freely...if you don't something is wrong.

Incidentally, when I was dealing with this, I heard 2 interesting things regarding the cause of the issue, that I had never heard here:

1. the guy who did the bodywork for me said that the area where the floor of the tray, the firewall and the wheel arch meet was never properly sealed up from the factory. He welded mine from both sides but he said it looked like the original relied on that seam-sealer type stuff.

2. an old-school, very experienced mechanic here told me that people using the wrong sized battery contributes to the problem. He said the original batteries were larger, and that smaller ones move around a little, wearing away the protective paint and zinc coating. At least I think that was the explanation...it was definitely to do with the battery size anyway.

I have no idea about the truth of these statements, I'm just repeating what I heard. One thing that's obvious is that sealer stuff in the corner is a magnet for moisture due to the rough finish from the factory.

superloaf

So attempting a repair on this area but there's a box area between the battery compartment and the fender which on my car keeps filling up with water. There are 3 rubber plugs which seal this compartment from the battery area. I'm not sure why mine is holding water. And not sure if there is a drain or if this compartment is not supposed to be exposed to water in the first place....

My problem is that this compartment fills with water and then it has corroded to allow the water to flow out into the area I'm trying to repair so it's hindering the fix and I'm worried about water leaking into this area once I've fixed the hole and causing further problems.

Here's a pic of the compartment I'm referring to: