A bit of preventative maintenance that may be of interest!

[Russbmw]

PLEASE BEAR IN MIND THIS WAS DONE ON A UK / RHD CAR, so presumably some things would be flipped for a US/ LHD car.

So, another little gem of BMW design glory (this also applies to F10 and F07 cars, if anyone's interested)

Noticed the other day (before the biblical rain here in the UK yesterday thankfully) that the car seemed to have collected a substantial amount of water in the cavity by the passenger side bulkhead. Enough that it required me to syphon it out with some tubing. Thankfully it wasn't on the drivers side, as this is where the main ECU lives, however on the passenger side, there's a whacking great plastic box that houses the HVAC fan and stuff that's all sealed up against the bulkhead, so still not great.

Anyway, you can guess where the drain is for this cavity? Yup, directly beneath the HVAC box. How do you get the HVAC box out, you ask? Simple! Remove the entire interior dash, as the fucking thing is bolt in from the inside! Nah...I'm good thanks.

Now, aside form this stupidity, there's another marvel of engineering. The large cavity is linked by an open channel to a smaller cavity which is hidden behind some plastic panels. The plastic panels have rubber sealing strips to keep water out (or as you'll see, in....genius!). The panel that seals this smaller chamber also houses a large rubber plug through the bulkhead, this is used to blank the hole where left hand drive cars would have the steering column).

In summary, when the drain holes get blocked beneath the HVAC box, that you can't remove, the water level rises and fills the hidden cavity where the bulkhead plug is. Back in the larger HVAC box cavity, there is a vent to the outside world behind the wing, so water does eventually find it's way out of that before it gets high enough to damage anything in the HVAC box. However, as the water level has already filled the smaller chamber (which has nowhere to drain...quality) this royally fucks the yellow bulkhead plug over time and can lead to an incomprehensible amount of water leaking into the car - that you'd be very unaware of until the carpets and backing foam have soaked up litres and litres of it. Less than ideal, as you can imagine.

So my first task was to check this smaller cavity to see what the hell was going on.

Inside the engine bay, to the right of the engine if you're facing the car there's a number of insulated plastic panels. The one you need to get to is the one where there's 3 or 4 hoses going through a rectangular rubber grommet.



It's held in by 4 torx screws and a locating lug. 3 you can see, and the 4th you'll just have to feel for as it's up out of sight, and the bolt screws in in the direction of the wing. It can be a bit stuck, so use a trim removal tool to break the seals - you'll see where they are in the pic below. Be careful as this plastic can be brittle so dont' tug on teh bottom corner too hard or it'll break, as I found out (but managed to glue the broke bit back on, and to be honest all the seals were still in tact and it probably woulnd't have made any different to anything if I hadn't).

Here's the piece once it's out. The tab bit at the top is where the rectangular hose grommet slides into, and you can see the plastic lug on the bottom right which locates into the chassis rail.



Here's the reverse side that seals against the bulkhead - you can see where the water has been trying to seep out at the bottom.



Best thing to do is drill a reasonable (10mm or so) diameter hole in this stupid-ass cover, so any water that gets behind it can get out. Bearing in mind this is just an emergency backup incase the main drain holes in the HVAC box cavity are blocked)



I also glued a plastic clip around the hole underneath the insulation, just to make it less likely for the insulation to prevent the water flow.



Here's the yellow plug in the bulkhead, and you can see the rectangular drain into this area to the right of it. Looks like I got to mine just in time, as the grommet already as a tide mark on it and you can see the rubber is starting to perish, although it did still feel like it was ok.



Anyway, clean out the area, clean the seals on the panel and put it all back together.

Knowing the main drain was blocked, I chucked some water down and was happy to see it all draining out of the new panel hole.

Now to sort the main drain, so hopefully nothing finds it's way down here anyway.

The main drain is impossible to get to without taking the HVAC box out, and it's also near impossible to inspect even with an endoscope on my phone, so figured the best way would to be to get at it from the other side.

Removing the wheel arch liner is simple enough and doesn't take long. Loosen the wheel bolts, jack the car up, remove wheel bolts and wheel, and then it's maybe 8 or so 8mm trim bolts and some push rivets on the wheel arch. These were a bit of a pain, because you have to push the centre pin in to allow the pins to be pulled out, and as you cant' see how far you've got left to push the pin, you inevitably show it all the way out and into the wing/sill. Not too much of a problem, as you can fish them out once the arch liner is off, but might be an idea to have a few spare new ones just incase.



The drains rubber flaps are either side of where the metal pipes pass through, on either side of the rubber oval bit, you can feel them with your finger.







I simply poked around and pulled out a few leaves and bits of junk. Then poured some water down again to check it was all free flowing, and it seemed it was. Happy days.

Re-assemble.

To give you an idea of timescales, removing the trim panel, cleaning, drilling and re-fitting could take not more than about 20-30 mins tops. Wheel arch liner removal, unblocking the drain and refitting everything is about 30 mins.

Definitely worth an hour of your time, in my opinion.

Hope that helps some people!

[ezmaass]

Great advice and thanks for sharing the detailed pictures.

[Russbmw]

No worries, thought I'd post something up as it was news to me, and I was glad I caught it before it manifested itself into a true ballache of a problem! 😂

[NINJA59]

The area of the yellow grommet is not an "emergency drain".

The centre two sections in the middle of the windscreen drain directly to that area in addition to the right hand side.

Usually most people get a wet rear carpet first due to this grommet failing as it is thinner

Furthermore this issue also applies to the Rolls Royce models (ghost, wraith and dawn) as they have the same design and grommet part number.

I would also clean the grommet at the base of the drivers side as it is also flapped like the passenger one. Over time bio film stops it from opening properly, it is slightly different in design terms as there is no pipework through it but exhibits similar issues.

I will also add there is drains on each inner wing side that run down the back of the wings, but they are half way or so up.... furthermore most cars will only have the active bonnet wiring there.

The main car DDE for 640d's is down the left hand side in the black box by the washer bottle. Not sure on petrol models.

[Russbmw]

What I said, and I'll say it again incase for some reason it was unclear ; when the main drain blocks, the water level rises and fills the area where the yellow grommet is. This water has nowhere to go and can damage that yellow grommet leading to leaks into the cabin when that yellow grommet fails.

What I also said was yes, the vent in the wing is there, but by the time the water level is that high and not draining completely, that yellow grommet is submerged and the only thing stopping water ingress into the cabin. So the wing vents should not be relied upon, in my opinion.

Hence it makes sense, in my opinion of course, to have some way for the water to get out, as checking the main drain is not blocked is not something you do all the time, nor is regular cleaning of the main drain easy to do on a regular basis. You're right about the drivers side being the same problem.



But hey, it's up to people what they want to do, I just thought I'd share my findings.

[dom3.0]

Good man, thanks! Looking forward to doing some DIY...

[dansonsmith]

Same problem.... leaves blocking main drain....wave machine in passenger footwell ��
Local garage did same as Russbmw and went up through wheelarch and charged me £100.....inc VAT not something I would try myself but obvs the right solution-great advice

[elvisisdog]

Anyone know if there is a similar cover for the drivers side (UK)?

I did the above to my car recently as my neighbour has a sycamore tree that likes to deposit is seeds and leaves over my cars. These perfectly fill the drainage holes do can make a right mess.

Some additional pictures to add to the ones above if people are struggling to see locations:

The cover is located at the back of the engine bay on the firewall:



Removed it looks like this:



What I found:



I found removing the top of the airbox for blower fan housing gave me enough room to clean out the leaves and remove some sound deadening trim (to dry out). My five year olds hands would have been much better suited to getting down in this region, but with a lot of swearing and removal of skin I managed to get my hand into points where I could extract the leaves and other debris. While the cover plate was off the yellow grommet area I flashed it through with several litres of water to I could feel no more leaves and everything was draining from where it should be.

Send a frustrating design to me, would make more sense to make the gully perforations smaller and better sealing up to do the problem doesn't move down into very hard to reach areas.

[PhilER]

This seems to be almost the exact same issue that affects the F10 5 series.

It only applies to RHD cars, as the yellow grommet is used to plug the hole where the steering column normally passes through the bulkhead on a LHD car.

I made the same modification as Russbmw on my 5 series to avoid the wet passenger footwell issue. There's a thread on it on the F10 forum I think.

[rasa bmw]

i left the felt cover off,and got rid of some of the seal around the cover,,water now drains out of it,i looked while pouring a watering can of water down it,had quite a bit of junk,leaves etc,,

[Smooth6]

I need to do this