E91 rear seat wet / water in battery compartment / water ingress search

AlexisM42 · 12-20-2021, 05:46 AM

Hi all,

E91 LCI from 2009 here.
Have had some water in the battery compartment, first discovered it in March this year. Started searching how the water got there, found some rust behind the trunk / boot rubber, so thought this was the cause. Had it fixed by BMW dealership. The body shop responsible told me that if the problem persists I should drill a small hole in the battery compartment.

Didn't have much rain after that, until past month. Huge downpours.
Noticed the water was still building up in the battery compartment. Took out battery, drilled two small (5mm) holes in the compartment, water drained out, touched it up with antirust paint, job done. Or so I thought..

Yesterday I noticed the lower part of the rear seat was wet. Took it out, the felt mat / carpet underneath was completely soaked.
The only part of the carpet that's wet is the center part of the carpet that sits the lowest (see pic attached)

Did some searching for common causes. Clogged sunroof drains: I don't have one.
Faulty antenna bracket: water should seep in through the antenna and come down through the roof. Wet marks should be visible on the headliner, not the case with my car. Removed centre dome light and had a peek, nothing wet or musty to be seen between headliner and roof.
Checked rear lights: seals seem to be fine, bolts tight, no signs of water ingress.
Checked antipressure flaps: perfect condition, nothing missing or broken.
Removed C Pillar plastics on both sides: no signs of water ingress.
Checked door rubbers and removed plastic part between door and seat, no signs of water ingress.
Removed the sides of the rear seat to check if the carpet underneath was wet: bone dry.

Found this video from a German car repair show tackling a similar issue with an E87: https://www.rtl.de/videos/woher-komm...37d312832.html

In this video I saw that the water entered through the antipressure flaps (broken in the case of the E87 in the video, mine are intact), water was building up in the trunk compartment. Under braking, the water was slushed towards the front and found its way to a cavity under the back seat, where eventually it seeped through the holes where the seat belts are attached.

Checked that and BINGO: I could suck out nearly half a liter of (clear) water with a syringe. There's definitely more water in there.
The fact that the water is quite clear leads me to believe that it's leaking from the top (raining in) rather than from the bottom (water ingress during driving).

I could see some water drops through the holes in the body located left and right from the far end of the trunk next to where the amplifier is (see picture attached).
Both sides could mean that water is entering from both sides and filling up the cavity. It could however also mean that it's only filling up on one side, and sloshing backwards towards trunk under acceleration.

Next step on my list is to remove the rubber cap found in the rear wheel well which I believe leads to the cavity under the rear seat. Need to check if I can drain more water from there using a tube.

That of course still begs the question of where the water is entering!

Anybody had a similar problem and found the cause of the water ingress?

Someone who used to work at BMW told me that window rubbers of the trunk windows located between C and D pillar sometimes also leak.. Haven't found anything like this online tbh.

Any help is very much appreciated!

nsjames · 12-20-2021, 10:26 AM

100% it migrates into the frame rails and then fills up in there and ends up in the back seat. park it nose high and use a shop vac to suck the water from the back of the framerails in the amp/battery compartments. Best way to get it all. There are plugs in the tops of the rails behind the rear seat back under the black plastic supports you can pull out as well to verify that you've gotten it all out, and spray the fluid film in there.

mine was sunroof drains.

Pull all the carpeting in the cargo area and lightly dust it with baby powder back there. it's messy, but the water tracks will show you where it comes from anyway.

AlexisM42 · 12-20-2021, 12:37 PM

Quote:

Originally Posted by nsjames

100% it migrates into the frame rails and then fills up in there and ends up in the back seat. park it nose high and use a shop vac to suck the water from the back of the framerails in the amp/battery compartments. Best way to get it all. There are plugs in the tops of the rails behind the rear seat back under the black plastic supports you can pull out as well to verify that you've gotten it all out, and spray the fluid film in there.

mine was sunroof drains.

Pull all the carpeting in the cargo area and lightly dust it with baby powder back there. it's messy, but the water tracks will show you where it comes from anyway.

Hi James, thanks for your reply!
Good point about parking it nose up. Our driveway is slanted and I usually park it nose down. Will change that up to see if water flows back from the cavity into the trunk compartments. When I roll backwards and brake hard I can hear the water slosh around.

Need to check if I can locate the plugs in the top of the rails you're talking about.
With the 'frame rails' do you mean the hollow metal construction on which the trunk carpeting lies?

Good idea about baby powder. I've thought about drawing some lines with chalk, but in order for that to work I'd need access to those points where I suspect the water is flowing, and the lowest points are usually not reachable.

smatanovic · 12-20-2021, 01:14 PM

When mine leaked, it was the seal around the panoramic sunroof, which leaked and overwhelmed the drains, and ended up filling the amplifier compartment with water. Thankfully, I didn't have water in the rest of the cabin.

I replaced the seal around the panoramic roof and it completely eliminated the leaks; and is much more quiet when driving, to boot.

Good luck!

nsjames · 12-20-2021, 03:04 PM

Quote:

Originally Posted by AlexisM42

Hi James, thanks for your reply!
Good point about parking it nose up. Our driveway is slanted and I usually park it nose down. Will change that up to see if water flows back from the cavity into the trunk compartments. When I roll backwards and brake hard I can hear the water slosh around.

Need to check if I can locate the plugs in the top of the rails you're talking about.
With the 'frame rails' do you mean the hollow metal construction on which the trunk carpeting lies?

Good idea about baby powder. I've thought about drawing some lines with chalk, but in order for that to work I'd need access to those points where I suspect the water is flowing, and the lowest points are usually not reachable.

pull all the back carpets out.
there's two black trim pieces that the carpet panels rest on. Pull those out. There's some push pins into the side panels and some screws in the floor IIRC, but you can pull them without pulling the side carpets out.
under there is the square "frame rails" that form the substance of the unibody. There's black plastic plugs in the top of them. Pull those out and voila, water.

the naked plastic cargo area floor is a separate piece, so check the seal there as well, but mine was stuck real well with seam sealer of some sort. So probably not.

I'm pretty sure that the plastic vent/rubber flap arrangement is below the amp compartment floor, so I'm not sure that's your problem.

FWIW my sunroof drains leaked enough water through the rear speaker to flood my amp and the whole framerail, but never showed a stain or hint of problem, so I wouldn't rule out the sharkfin until you hit it with the hose from every angle and check.

Tambohamilton · 12-20-2021, 03:30 PM

Sorry I'm not going to be any help, but the whole "just drill a hole in the battery compartment" thing winds me up! Water isn't supposed to get there, so drilling holes isn't going to fix the problem. Sigh.

Good luck getting yours actually fixed

nsjames · 12-20-2021, 04:15 PM

Quote:

Originally Posted by Tambohamilton

Sorry I'm not going to be any help, but the whole "just drill a hole in the battery compartment" thing winds me up! Water isn't supposed to get there, so drilling holes isn't going to fix the problem. Sigh.

Good luck getting yours actually fixed

it's a BMW touring.

we're 3/3 for water leaks in three different models in my family.

so maybe water IS supposed to get in there.

nsjames · 12-20-2021, 04:17 PM

and it may be worth pulling the amp out of it's bracket before you park it nose up.

they don't like the water.
it's a nice system for alerting you to the water leaks though.

Tambohamilton · 12-20-2021, 04:34 PM

Quote:

Originally Posted by nsjames

it's a BMW touring.

we're 3/3 for water leaks in three different models in my family.

so maybe water IS supposed to get in there.

unlucky. I'm waiting for water ingress in the back of mine, but it's not happening yet... 14 years, so far so good!

AlexisM42 · 12-22-2021, 12:13 PM

Quote:

Originally Posted by nsjames

pull all the back carpets out.
there's two black trim pieces that the carpet panels rest on. Pull those out. There's some push pins into the side panels and some screws in the floor IIRC, but you can pull them without pulling the side carpets out.
under there is the square "frame rails" that form the substance of the unibody. There's black plastic plugs in the top of them. Pull those out and voila, water.

the naked plastic cargo area floor is a separate piece, so check the seal there as well, but mine was stuck real well with seam sealer of some sort. So probably not.

I'm pretty sure that the plastic vent/rubber flap arrangement is below the amp compartment floor, so I'm not sure that's your problem.

FWIW my sunroof drains leaked enough water through the rear speaker to flood my amp and the whole framerail, but never showed a stain or hint of problem, so I wouldn't rule out the sharkfin until you hit it with the hose from every angle and check.

Thanks again!

However, I decided to first see if I could drain the remaining water from below.
Jacked up the car on the rear diff, took off the wheels, first took off rubber caps left and right from the strut. Signs of water, but no water left for me to suck out.

Then made my way further down under the car. First took off rubber cap next to what I think is the subframe mount, sitting almost dead above the muffler. Wiggling it with a flatheaded screwdriver already made it drip.. Taking it out made it rain!
On the passenger side (battery compartment side) the same rubber cap was holding back even more water. Got a nice face full

Decided to leave those two rubber caps out while I drive around tonight and tomorrow. Weather forecast says no rain. That way the remaining water gets a chance to slosh out through those holes.

A definite recommendation for anyone experiencing this problem who wants to already drain out the existing water!

Might have ruled out the rear lights a bit too quickly as well. Saw a few fresh drops in the battery compartment on the far end (closest to the boot lid / rear light) and some very early signs of corrosion. Will check some tutorials on how to remove rear lights tomorrow and hopefully find the time to do so. Would be awesome if I could have this fixed with only new rear light seals. Would make the most sense also tbh, having had a rear impact that needed a new light, they might have re-used the old rubber seal..

Meanwhile I'll place an electric stove in the back tomorrow in hopes to fully dry out the carpet before re-installing the rear seat bottom. With most of the water now gone, I suspect not having to worry about a wet rear bench in the (very) near future.
The rear bench smells a bit musty on the sides though. Any ideas or tips to make smell minty fresh again?

Some pics attached!

AlexisM42 · 12-22-2021, 12:15 PM

Quote:

Originally Posted by Tambohamilton

Sorry I'm not going to be any help, but the whole "just drill a hole in the battery compartment" thing winds me up! Water isn't supposed to get there, so drilling holes isn't going to fix the problem. Sigh.

Good luck getting yours actually fixed

Yeah I agree. However two weeks ago I was fed up (without even knowing about the rear bench issue) and decided to get it over with and drill those holes. I feel kind of bad doing so now

However, I made sure to apply a thick layer of antirust paint to the holes so shouldn't be a problem in the future.

But indeed worrysome that the main body shop guy at the BMW dealership gave this as a tip

nsjames · 12-23-2021, 12:21 PM

do you have a dehumidifier?
put it in there with it all closed up and let it go for a time to dry stuff out.

I used my portable AC unit which had the benefit of a ducted hot air output I shoved under things.

I won't lie, my tail gate lamps got sealed with weatherstrip sealant. New gaskets still didn't get them 100%. I did it knowing that I will need new gaskets if I ever have to pull them out again.
If they're leaking, check the seam in the tailgate, mine was starting to rust inside. I hosed the whole thing down with fluid film. Access is impossible for proper rust repair.

edit:
and while you're taking hatch plastics apart, go ahead and pull the black trim pieces off the side. You'll probably find clogged drains and rust. Worst rust on my whole car was there. I ground it all off and converted it and painted it all black and put the trim pieces back.

3noob3 · 07-05-2023, 09:28 PM

I just realized I had the same problem as you because I extract a lot of water from the two holes in the backseat. Wondering how you deal with this issue, also is this due to the inflow from the gap in the car?

My model is E91 touring.(no sunroof)

BSpain · 08-08-2024, 06:05 PM

Did anyone manage to find the cause of the water getting into the rear chassis rails?

I've got water getting in the rear chassis rails, and from there it leaks into the battery compartment and amplifier compartment.

I emptied out the chassis rails, took the rear crash bar off and dried it all out with a heat gun and rags on a pole. Then a few days later after some rain I checked it again and found water in the chassis rails again but only a tiny dribble in the amplifier compartment, which appears to have seeped out of the seams of the chassis rail.

So it is definitely getting into the chassis rail somehow and then seeping into the compartments from there. However I cant find how it's getting into the rails.

12-20-2021, 05:46 AM	#1
AlexisM42 New Member 5 Rep 6 Posts Drives: E91 318D LCI Join Date: Jan 2021 Location: Belgium iTrader: (0)	E91 rear seat wet / water in battery compartment / water ingress search Hi all, E91 LCI from 2009 here. Have had some water in the battery compartment, first discovered it in March this year. Started searching how the water got there, found some rust behind the trunk / boot rubber, so thought this was the cause. Had it fixed by BMW dealership. The body shop responsible told me that if the problem persists I should drill a small hole in the battery compartment. Didn't have much rain after that, until past month. Huge downpours. Noticed the water was still building up in the battery compartment. Took out battery, drilled two small (5mm) holes in the compartment, water drained out, touched it up with antirust paint, job done. Or so I thought.. Yesterday I noticed the lower part of the rear seat was wet. Took it out, the felt mat / carpet underneath was completely soaked. The only part of the carpet that's wet is the center part of the carpet that sits the lowest (see pic attached) Did some searching for common causes. Clogged sunroof drains: I don't have one. Faulty antenna bracket: water should seep in through the antenna and come down through the roof. Wet marks should be visible on the headliner, not the case with my car. Removed centre dome light and had a peek, nothing wet or musty to be seen between headliner and roof. Checked rear lights: seals seem to be fine, bolts tight, no signs of water ingress. Checked antipressure flaps: perfect condition, nothing missing or broken. Removed C Pillar plastics on both sides: no signs of water ingress. Checked door rubbers and removed plastic part between door and seat, no signs of water ingress. Removed the sides of the rear seat to check if the carpet underneath was wet: bone dry. Found this video from a German car repair show tackling a similar issue with an E87: https://www.rtl.de/videos/woher-komm...37d312832.html In this video I saw that the water entered through the antipressure flaps (broken in the case of the E87 in the video, mine are intact), water was building up in the trunk compartment. Under braking, the water was slushed towards the front and found its way to a cavity under the back seat, where eventually it seeped through the holes where the seat belts are attached. Checked that and BINGO: I could suck out nearly half a liter of (clear) water with a syringe. There's definitely more water in there. The fact that the water is quite clear leads me to believe that it's leaking from the top (raining in) rather than from the bottom (water ingress during driving). I could see some water drops through the holes in the body located left and right from the far end of the trunk next to where the amplifier is (see picture attached). Both sides could mean that water is entering from both sides and filling up the cavity. It could however also mean that it's only filling up on one side, and sloshing backwards towards trunk under acceleration. Next step on my list is to remove the rubber cap found in the rear wheel well which I believe leads to the cavity under the rear seat. Need to check if I can drain more water from there using a tube. That of course still begs the question of where the water is entering! Anybody had a similar problem and found the cause of the water ingress? Someone who used to work at BMW told me that window rubbers of the trunk windows located between C and D pillar sometimes also leak.. Haven't found anything like this online tbh. Any help is very much appreciated! Attached Images
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12-20-2021, 10:26 AM	#2
nsjames Brigadier General 2466 Rep 4,328 Posts Drives: 08 328xi Touring Join Date: May 2017 Location: ohio iTrader: (0)	100% it migrates into the frame rails and then fills up in there and ends up in the back seat. park it nose high and use a shop vac to suck the water from the back of the framerails in the amp/battery compartments. Best way to get it all. There are plugs in the tops of the rails behind the rear seat back under the black plastic supports you can pull out as well to verify that you've gotten it all out, and spray the fluid film in there. mine was sunroof drains. Pull all the carpeting in the cargo area and lightly dust it with baby powder back there. it's messy, but the water tracks will show you where it comes from anyway.
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12-20-2021, 01:14 PM	#4
smatanovic First Lieutenant 199 Rep 331 Posts Drives: 2022 i4 eDrive 40 mSport Join Date: Oct 2020 Location: The 215 iTrader: (0) Garage List 2022 i4 eDrive40 [0.00]	When mine leaked, it was the seal around the panoramic sunroof, which leaked and overwhelmed the drains, and ended up filling the amplifier compartment with water. Thankfully, I didn't have water in the rest of the cabin. I replaced the seal around the panoramic roof and it completely eliminated the leaks; and is much more quiet when driving, to boot. Good luck!
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12-20-2021, 03:30 PM	#6
Tambohamilton Brigadier General 3295 Rep 4,223 Posts Drives: E91 330d Join Date: Apr 2019 Location: Herefordshire iTrader: (0)	Sorry I'm not going to be any help, but the whole "just drill a hole in the battery compartment" thing winds me up! Water isn't supposed to get there, so drilling holes isn't going to fix the problem. Sigh. Good luck getting yours actually fixed
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12-20-2021, 04:17 PM	#8
nsjames Brigadier General 2466 Rep 4,328 Posts Drives: 08 328xi Touring Join Date: May 2017 Location: ohio iTrader: (0)	and it may be worth pulling the amp out of it's bracket before you park it nose up. they don't like the water. it's a nice system for alerting you to the water leaks though.
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12-23-2021, 12:21 PM	#12
nsjames Brigadier General 2466 Rep 4,328 Posts Drives: 08 328xi Touring Join Date: May 2017 Location: ohio iTrader: (0)	do you have a dehumidifier? put it in there with it all closed up and let it go for a time to dry stuff out. I used my portable AC unit which had the benefit of a ducted hot air output I shoved under things. I won't lie, my tail gate lamps got sealed with weatherstrip sealant. New gaskets still didn't get them 100%. I did it knowing that I will need new gaskets if I ever have to pull them out again. If they're leaking, check the seam in the tailgate, mine was starting to rust inside. I hosed the whole thing down with fluid film. Access is impossible for proper rust repair. edit: and while you're taking hatch plastics apart, go ahead and pull the black trim pieces off the side. You'll probably find clogged drains and rust. Worst rust on my whole car was there. I ground it all off and converted it and painted it all black and put the trim pieces back.
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07-05-2023, 09:28 PM	#13
3noob3 Registered 0 Rep 1 Posts Drives: BMW 320i touring Join Date: Jul 2023 Location: New Zealand iTrader: (0)	Hello Alexis! I just realized I had the same problem as you because I extract a lot of water from the two holes in the backseat. Wondering how you deal with this issue, also is this due to the inflow from the gap in the car? My model is E91 touring.(no sunroof)
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08-08-2024, 06:05 PM	#14
BSpain Registered 2 Rep 2 Posts Drives: BMW E91 335i Join Date: May 2024 Location: Auckland, NZ iTrader: (0)	Did anyone manage to find the cause of the water getting into the rear chassis rails? I've got water getting in the rear chassis rails, and from there it leaks into the battery compartment and amplifier compartment. I emptied out the chassis rails, took the rear crash bar off and dried it all out with a heat gun and rags on a pole. Then a few days later after some rain I checked it again and found water in the chassis rails again but only a tiny dribble in the amplifier compartment, which appears to have seeped out of the seams of the chassis rail. So it is definitely getting into the chassis rail somehow and then seeping into the compartments from there. However I cant find how it's getting into the rails.
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