Good or Bad idea? Drilling a drain hole
 

I am still struggling with water in the car (passenger rear floor) even after cleaning all the drain holes in the trunk and under the battery. The floor still gets wet when it rains.

I can't afford to change all the seals so I am thinking of pulling the carpet and drilling drainage holes on the floor with multiple coats of rustoleum.

Is this a really bad idea? all input is appreciated.

bad idea, need to fix the issue, or good idea if and only if you are going to eventually fix the issue.
any water inside is not good, and holes into the cabin are bad for many reasons, CO2, noise, you will not be able to use any type of covering over footwell

While it is not a good idea if you do it this way you could be OK...

Drill one hole. Insert a piece or rubber tubing through the hole so that it extends about 2 inches under the car.
Seal the hole around the tubing with silicone sealer on both sides of the floor pan.

The thought is that while water can drain down from the floor, the tube will prevent most splashes from going through the hole and wetting the floor.


Good luck!

Lift up the carpets and see if there's a drain hole already.

I know in my 123s there is a rubber cap that plugs a drain hole. You can pull it out to drain the floor of water if needed. I actually think the plug has 3 little holes in it too so it doesn't need to be pulled out. If yours has this drain hole and plug, maybe the plug has dirt plugging up the holes.

At any rate, I'd like to know if it has them if you don't mind looking and reporting back. I plan to buy a 300SDL in the very near future.

+1. What I'd do is pull the fullsize round rubber drain plugs that exist in the rear footwells, and replace with the ones that have three small holes in them which serve as actual drains (like are in the trunk and already on the car for draining the rockers).

This will serve as a drain with decent closure from the elements. You can get them at the dealer for just a few dollars, and Im sure Phil can source them too. They may be on fastlane.

Did you clean the drain holes under the hood hinges?

yes. there was about a quarter inch thick layer of dead leaves and pine needles.

i am now wondering if removing all that was enough. i'll have to the do the garden hose test soon to check.

where is the water supposed to drain? does the water go behind the fender? i wish i could remove the fender or something to see

That's CO (Carbon Monoxide) that you're worried about. We'd all be dead if CO2 was poisonous. And diesels produce far less CO that gassers, so it's not even much of a problem. I also don't think these holes would be large enough to make a difference in any of those factors, especially with a carpet over it.

Does it leak when it rains, even if you're not driving? I was trying to find a leak, did the hose test, nothing. Took it for a drive with sister in the back seat and no carpets. Once i drove through a puddle, water gushed in:eek:

If it were me, I'd track down the problem or live with it for the time being. Drilling holes might not even solve the problem, because your carpets would probably soak up any water that gets there.

There could be some rot in one of the nooks and crannies in the firewall that the water is coming in through. That's where my leak is, not immediately noticible until I pulled all of the carpets out one day to clean them and while they were out I was cleaning the engine compartment and noticed a decent stream of water coming into the passenger footwell. :o

You need to find the leak before the floor rusts. It will be a constant hassle/threat until you stop the leak. If you can't stop the leak, remove the carpet and any padding so that it doesn't hold moisture & cause rust. Treat with a can of POR 15 (small size) if there is any rust now.

I think it's a bad idea because it doesn't fix the problem, but it's better than having a water puddle in the rear passenger area. There is a drain hole in the front passenger side but not in the rear passanger area. I would drill a very small hole just so that water doesn't collect in inches.

The first place to look is at the windshield gasket. Unless it is most unusual it will be leaking like a sieve.

Then you can choose to replace the gasket or clean the crack very well and caulk it with black silicone.

That's where mine was leaking. Hole just under the battery tray. Took almost a year to find it. Had the carpets out (to dry) and drove through a car wash. Water came in the front passenger side and flowed to the back. I did drill a 1/4" hole to let the water out until I found the problem. It worked. Carpet covers the hole and this thread reminds me I can close that hole now. There was a drain plug but it wasn't at the lowest point and it was closed.

Drilling a hole in the very well protected floor pan introduces a foothold for rust to start. I would not do that.

Where is the water supposed to drain?
 

I found a soft rubber tube coming down by the back of the wheel well (W123 84 300D) that I assume is the end of the drain that originates in the rear of the engine compartment. I could be wrong, as maybe it comes from further up, like the the sunroof or the windshield channel. Wherever, I found it was plugged with debris and mud. I poked that stuff, as I am sure it was holding back water.