W124 Coupe Driver Footwell Water Leak -doesn't seem to be drains

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New Member
Apr 15, 2023
300 CE
Hi all, I've been trying to figure out where the water is coming from in the driver-side footwell in my 300CE. I've cleaned out the two side windscreen drains which were blocked up -and the sunroof drains- and they seem fine. But water keeps ingressing. In the engine bay, the grommet inside the area by the fuse box looked possibly worn out and I stupidly gave it a poke -now it's fallen into the hole.

Engine bay had been attacked by a bloody rat when parked during winter nights without me realising until it nibbled through a vacuum hose. (Rat problem dealt with.) I had tried to clean out the engine bay previously of its stink and am wondering if water got in through that grommet. But the water inside seemed too much to have been from that event (and the majority of the water drained straight out on to the driveway when cleaning in the engine bay). When I found the water inside, the soundproofing under the carpet was soaked and the rust damage suggests a much longer problem. I am a bit panicked as to where that grommet hole actually goes and am worried if there's water sat inside some sort of chassis crevice behind the wheel well.


It's been doing this long enough that it's rusted a hole (I filed out the rot) though one corner nook which I want to get welded but need to make sure the leak is stopped. (Thankfully the surface rust around it on the underside of the car sanded to bare metal easily.) I've seen water coming into the foot well through the black plastic housing from up in the engine/fender, but I'm not sure where that emerges in the engine bay. Worrying as well was that another rust patch seemed to trickle water for ages before it stopped and I'm wondering if that comes from wherever that grommet lead or if there's some cavity somewhere... I'd have thought there'd be nothing under it but the underside of the floorplan, unless the rust there has been acting like a sponge.


Something round the back is leaking is well as I found moisture under the rear seats where the relays for the windows chatter away. But the main leak seems to be from the front as I witnessed water dribbling out of that black plastic housing even after cleaning the drains.

I have removed the wiper trim to check the central drain under the blower motor. The rubber funnels seem fine, drain wasn't blocked and the blower motor area was dusty-dry despite the rain, so don't think it's ever filled up or overflowed.

I've been stupid and had no idea about things like drain maintenance but doing my best and learning as I go. Hope this isn't curtains for the car because for all the things that have gone wrong with it still cheers me up when I see it. Any advice as to where that black plastic housing leads, where that grommet by the fusebox goes to, or what might be causing all this besides the drains would be really appreciated.
This isn't much use to you but my coupé has an occasional wetness in that area. I checked recently after serious downpour. Bone dry.

I thought it might be coming up from under so I looked after a drive on very wet roads. Bone dry.

The symptom is that the deep foam section of the carpet underlay is dripping wet. Only that bit. The rest of the carpet underlay is dry.

Some years ago I was getting absolutely sodden carpets on both sides. I checked all drains and they seemed OK. I poured water into the sunroof - no wetness.

Then the windscreen was changed and minor corrosion fixed. Problem solved aside from this occasional wetness as above.

Mine's a LHD so it's in the passenger side.

Let us know if you find a fix

Good hunting.

The bulkhead is the first area i would look .And the other area - can be big a problem on the W124 .It is under the battery tray . Screen is another area it will seap under the window rubbers I am sure there is a drain in the heater box area .
Thanks lads, the windscreen rubber lining does seem shrunken under the chrome trim on both the front and the back. I think Optimus is on to something with the bulkhead too. I'm pretty sure now the water's been making its way down these wires that lead to the central locking pump under the rear seats. Trying to figure out where they emerge in the engine bay and if there's some sort of rubber gasket that's perished. Suspecting it might be directly under the fuse box?ingresspoint.jpg

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