[paloalotpeter]

My 2009 335D has an odd problem. The rear passenger seat footwell area is soaked. What is strange is that I can't see any evidence of how the water is getting in. The sides of the carpet all around the area (e.g. near the rear passenger door) are dry; the front passenger seat carpet is dry, and there's no evidence of water dripping down from the roof/sunroof. So I have no idea where the water is coming from.

I have looked through the forums and have tried a few things
- I unclogged a blocked drain on the passenger side of the sunroof
- I unclogged both drains under the hood (where there's a removable plastic grid to catch leaves, etc)
- I have sprayed water with a hose but can't see any signs of water coming in.

None of these have helped.

The only thing I've noticed is that the floor seems to be particularly wet around the area near the electrical cable that powers the passenger seat and the air vent that feeds air to the back seat. I don't know if there's any way that water could end in in that air vent and run all the way to that one area - the rear seat behind the driver is bone dry.

Would love any insights on where the water might be coming from. TIA.

[N52bigblock]

Have you had any window regulators replaced lately? I have seen a lot of water leaks like you are describing which are caused by the door sound insulation (on the door behind the door panel) not being refitted properly or torn by somebody who has replaced a window regulator. It is important that these are resealed correctly and not damaged as they also act as a water seal. The repair instructions are here.
https://www.newtis.info/tisv2/a/en/e...-front/42wVBxl
The other important thing is the door panel clips. Some of them have seals on them which quite often get lost when someone has the door panel off. Make sure the clips are all there and have the little seals on them otherwise they will leak in heavy downpours.

[N52bigblock]

Door panel clips with seals

[paloalotpeter]

Thanks for this suggestion. I haven't had any work done on the rear door at all. But maybe something got torn or damage through regular wear and tear. But if this is the problem, wouldn't the carpet that's right underneath the door be wet too? It seems that only the carpet at the very lowest area is wet - the sides where the carpet goes up and tucks under the door, up to the center console, etc all seem to be dry.

[paloalotpeter]

Using the (wonderful) instructions you linked to, I was able to remove the rear door panel. The sound insulation is completely intact and both it and the inside of the door panel seem to be bone dry. Given how tricky it seems to be to remove the sound insulation, and the fact that it's dry, I decided not to go any further.

Would love any other ideas.

[N52bigblock]

Check the front ones as well. I have seen it quite a few times before where the front sound insulation is torn and it fills up the only the rear footwell. Maybe due to being parked on a hill. Sometimes the sound insulation just lifts up by itself. Make sure it is stuck down properly and remember the door panel clips with seals also. It's definitely worth checking the fronts in my experience.

[N52bigblock]

Originally Posted by paloalotpeter

Thanks for this suggestion. I haven't had any work done on the rear door at all. But maybe something got torn or damage through regular wear and tear. But if this is the problem, wouldn't the carpet that's right underneath the door be wet too? It seems that only the carpet at the very lowest area is wet - the sides where the carpet goes up and tucks under the door, up to the center console, etc all seem to be dry.

The carpet thats right underneath the door seems to dry out quite quickly. Another tip is to remove the lower part of the rear seat and lift the carpet up. There is a lot of foam insulation bonded to the carpet. And that holds a huge amount of water. It's very hard to dry out unless the weather is warm or you use a heater of some sort.

[nsjames]

since you're probably going to have to pull/lift the carpet to get it to dry properly, go ahead and do that, then dust the sheetmetal lightly with some baby powder.

now go through a car wash.

follow the water tracks back to your leak.

it is time intensive to do it that way, but you're going to end up with a bad smell in the carpet if you don't pull it up and get the padding dry quickly.

[e90yyc]

James’ suggestion is great, but the process can be made even shorter (and more enjoyable) by using cocaine instead of baby powder. I usually start with a couple grams—maybe an eight-ball if I’m really determined to find the leak. After you’re done you can just chalk up any dry coke in the footwell into a couple nice lines. As for the wet stuff, I usually scrape it up and use it to make some crack.

Just my two cents

[N52bigblock]

Originally Posted by e90yyc

James’ suggestion is great, but the process can be made even shorter (and more enjoyable) by using cocaine instead of baby powder. I usually start with a couple grams—maybe an eight-ball if I’m really determined to find the leak. After you’re done you can just chalk up any dry coke in the footwell into a couple nice lines. As for the wet stuff, I usually scrape it up and use it to make some crack.

Just my two cents

[paloalotpeter]

Thanks for the legal and not so legal suggestions ;-) I will try the rear seat step first.

[paloalotpeter]

Just to let any other people who might be dealing with this - the problem was finally traced to the passenger side drain under the hood. I thought I had unclogged it but the shop I took it to blasted it with a high pressure air hose and that fully unblocked it. It seems the water was coming in, snaking down the front passenger door then running into the rear passenger footwell.

Thanks to everyone for the help and suggestions.

[sfarisminhas]

Originally Posted by neilj35

Door panel clips with seals

Originally Posted by neilj35

Door panel clips with seals

This is strange. On some doors I have seen the opposite. As you can see there are 5 grey clips and 4 white ones. Which isn't the same as what you have posted.

[jarsdad1]

Can you post a picture of the door (inside) now?

[sfarisminhas]

I'll post it when I get home from work. You will clearly see watermarks under where the clips are. I think there is a significance as to why grey clips are used in one area and why white are used in another. The grey clips have seals and the white ones have washers. In the past I wasn't aware and just used whatever seals/washers were lying around and maybe it hasn't done the job properly.

[jarsdad1]

Originally Posted by sfarisbradistan

I'll post it when I get home from work. You will clearly see watermarks under where the clips are. I think there is a significance as to why grey clips are used in one area and why white are used in another. The grey clips have seals and the white ones have washers. In the past I wasn't aware and just used whatever seals/washers were lying around and maybe it hasn't done the job properly.

Ok. Sounds like a vapor barrier problem. Check that.

[sfarisminhas]

Originally Posted by jarsdad1

Ok. Sounds like a vapor barrier problem. Check that.

I've put new vapour barriers and new butyl on both doors

[sfarisminhas]

You can see in the pics where the clips are that there are watermarks under the door clips towards the bottom left and centre.

[jarsdad1]

I would re-check the seak on the vapor barrier on the door. I had to reseal mine 3 times.