Hey guys,


So I recently got serious about getting my car to stop leaking water inside. Needless to say, the PO was not aware of the drains under the hood and they were all clogged. This created a bit of rust through under the battery tray, and some rust through the driver side hood hinge pocket. On top of that, the PO had the windshield seal replaced, but he used a non-genuine MB seal that wasn't quite a perfect seal.

I did extensive cleaning and rust treatment to the metal, and layed multiple layers of fiberglass over the affected areas with a thick coat of resin. By applying lots of water specifically to those water channels, I was able to verify that did the trick for those drain spots. I found the window seal to leak after that, so I used the flowable silicone to seal that up. I was able to verify that resolved the windshield seal leak.

I know those might not be the most preferred, permanent solutions, but no need to debate that. I can confirm the water drains are sealed.

During the time the water was leaking, it rusted through two spots of the floor on the passenger side. One was at the front side kick wall of the passenger floorboard, right around the plastic cover for the vaccum lines. It rusted through a bit. I pulled up a good portion of the floor stuff and punched out the rotted metal and did the rust treatment to seal up the metal. The other spot is at the very rear of the passenger floorboard, on the side wall that runs under the back door. Did the same thing, also left a few small holes. I did the rust treatment, but I have yet to fiberglass over those holes.

Since sealing up all the water drain areas, I did lots of hose testing, made sure the sunroof drains were clear, etc. From my observations of hosing the car down, it's water tight. However, I drove it in heavy rain the other day, went through various puddles, etc and while the front floorboard areas were dry as a bone, there was the smallest puddle in the back passenger side, and the carpet over the little rust holes in the back was damp.

So my question is, do I possibly still have a leak from the front, or is there a way that water is coming up from the under the floor and entering through those holes that I haven't sealed up yet?

I know how water always ends up in the back on these cars, but after how much I've worked on this, I know that the front floorboard will usually show a mild dampness as evidence of the water passing through. But I see no evidence of water coming from the front to the back, it's as if it originates in the back.

Sorry about the essay, just wanted to express all the bases I've covered. haha

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1984 Mercedes-Benz 300D

I would say your holes in the floorboard are causing your wetness in the back. If you go at the holes with the fiberglass that should seal it up nice.

Driving in the rain and squirting with a hose are totally different, it's like the difference between drizzle and a hurricane. The aerodynamic effects causes the whole underside of the car to be bathed in high pressure water and it finds it way into any and all openings.

Just beware, that is a major structural area and i would take great care to ensure that area is sound. The rust on a 123 has a nasty way of sneaking under the coating and what seems like a little soft spot can turn into a whole region of iron oxide dust bound together by an undercoating and sound deadening sandwich.

My 123 had the same problems and it is unfortunately a byproduct of the non-galvanized steel they had at the time the car was made. I sold it to greazzer, and even though I thought the car had some issues it was 90% better than the one he had.

124s and newer were made with galvanized steel which is much more rust resistant.

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The OM 642/722.9 powered family
Still going strong
2014 ML350 Bluetec (wife's DD)
2013 E350 Bluetec (my DD)

both my kids cars went to junkyard in 2023
2008 ML320 CDI (Older son’s DD) fatal transmission failure, water soaked/fried rear SAM, numerous other issues, just too far gone to save (165k miles)
2008 E320 Bluetec (Younger son's DD) injector failed open and diluted oil with diesel, spun main bearings (240k miles)

1998 E300DT sold to TimFreeh
1987 300TD sold to vstech

Check the HVAC drain hose inside behind the center console. Its made of foam. You'll probably find it in pieces. I replaced mine with a piece of rubber hose and that fixed my wet floor problem..

Ah, that makes a lot of sense. I figured something about driving in rain would do that. So I'll seal up the holes and keep an eye on it.

And that's really interesting on the steel. I always wondered why these older models were so bad about rusting. I'll keep that in mind. Thanks!

As of right now, my HVAC system is far from functioning. haha But when I get around to working on it, I'll keep that in mind to look out for!


So I found my tail-light seals are a little leaky. If needbe, I can seal those up to, but is there any good replacements made nowadays? I looked online, but didn't see any.

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1984 Mercedes-Benz 300D

What size hose did you use? Thanks

Go to Home Depot or Lowes and buy a replacement dishwasher drain hose. The kind with the big rubber boot that fits on the nipple on the disposal. Cut off the hose from the disposal fitting and use the the disposal piece for the drain. This fits just right on the a/c box nipple and is the right length to poke through the floor. Works great.

__________________
The OM 642/722.9 powered family
Still going strong
2014 ML350 Bluetec (wife's DD)
2013 E350 Bluetec (my DD)

both my kids cars went to junkyard in 2023
2008 ML320 CDI (Older son’s DD) fatal transmission failure, water soaked/fried rear SAM, numerous other issues, just too far gone to save (165k miles)
2008 E320 Bluetec (Younger son's DD) injector failed open and diluted oil with diesel, spun main bearings (240k miles)

1998 E300DT sold to TimFreeh
1987 300TD sold to vstech