B8.5 S4 Avant - Water leak in boot

[g00se]

Hi team - HNY and all that!

So back when I did my last track day I decided to empty my boot of tools etc. into the paddock I had rented.. I then decided to go a little further and remove the dogs bed/boot liner/boot floor panel/spare wheel = race car lol

To my horror my battery and B&O sub were sat in about 1/4" of water!!!

I soaked it all up with paper towel, and carried on about my track day, but kept checking and there was always more spots dotted all over the place - rather than seeing one clear point of entry.

Over the last few weeks/months there's barely been a dry day (just my luck!), but having done some research I've seen this is quite a common fault caused by several potential failures:-

1. Pan roof drains (I don't have a pan roof - so its not this)
2. Rear light seals (all foam inside the light clusters is dry)
3. Rear air pressure vents - behind rear bumper (as per above - all dry around these areas)
4. Rubber seal around boot opening (no sign of water ingress)
5. Rear screen washer (no sign of water in the tail gate)
6. Rear screen seal (no sign of water ingress)

So the investigation gathered momentum and I gutted the entire boot, all trim/carpet etc.. and found there are 2x rubber bungs/grommets in the boot floor; to which I believe they are there to let excess primer escape when the shells are dipped in paint (!)

So I dried the boot again, then taped some paper towel over the grommets, and went for a 10 min drive on a day when it wasn't raining but the roads were wet.. and this was the result:-

Pretty sure both these bungs have failed, and the air pressure under the car is forcing them upwards and allowing rain water to spray around everywhere god knows how long they've been like that?! I've never had any condensation in the car, so would never have known had I not removed the spare.

Have ordered OEM replacements from Stoke Audi Parts (£12 delivered), and I think I will fit them with extra sealant... the bigger question is how did they both fail ???

I need another dry day so I can get under the car to see if all heat shield is all still in place, as I wondered if the heat from Scorpion exhaust had caused them to shrink/fail?!? Am grasping really haha

Oh well, lesson to us all here I guess.. check your rear bung holes regularly

goose

 

[spartacus68]

Interesting. That's a new one. Well spotted as your amp is in the boot, etc.

I've been in the boot on my B9 and B8 Allroads over the last couple of months adding new batteries and chasing a never-ending issue with panoramic roof on the B8 which I thought I'd sorted and yesterday there was drips of water onto the centre console, but on a plus point both corners on A pillar and importantly the carpets are bone dry. The weather has been atrocious recently and we've yet to have a dry day, so unfortunately these sort of faults show up.

If you are looking for a decent marine grade sealant (belt and braces approach) - then Sikaflex 291i could be used in conjunction with the new bungs. You can clean of excess with white spirits. Use nitrile gloves as the damn stuff gets everywhere. Comes in smaller tubes (70ml) black or white. Clean with alcohol wipe first prior to applying.

 

[Ajwhite]

@g00se how's the boot looking now?

Sent from my VOG-L09 using Tapatalk

 

[g00se]

Interesting. That's a new one. Well spotted as your amp is in the boot, etc.

I've been in the boot on my B9 and B8 Allroads over the last couple of months adding new batteries and chasing a never-ending issue with panoramic roof on the B8 which I thought I'd sorted and yesterday there was drips of water onto the centre console, but on a plus point both corners on A pillar and importantly the carpets are bone dry. The weather has been atrocious recently and we've yet to have a dry day, so unfortunately these sort of faults show up.

If you are looking for a decent marine grade sealant (belt and braces approach) - then Sikaflex 291i could be used in conjunction with the new bungs. You can clean of excess with white spirits. Use nitrile gloves as the damn stuff gets everywhere. Comes in smaller tubes (70ml) black or white. Clean with alcohol wipe first prior to applying.

Ugh.. this saga continues AJ !

I never got round to fitting the new bungs as when I got under the car the old ones both looked perfect and seating flush. I did go ahead and liberally spread some clear silicone sealant on both the underside and inside the boot.. thinking that would be the end of it.. alas :/

Another 60 mile drive and more water appeared.. a little less than before, but I cant tell if that's just because it was a shorter journey, or a drier day.

So I picked up some of those microwavable silica gel bags from Halfords and threw them in the boot.. hoping that the above may just have been residual leftover water. Seems to have been dry in there for a week, so i took the bags out and nuked them, and they were soaked! Clearly they had been absorbing something!!

So i drove without the bags.. and more water appeared *sigh... again less water, but again i don't know if its just because it was drier last week.

So here we are.. its getting rainier again up here in the NW so I'll do some more experimentation; i really feel like getting a mate to drive whilst i sit in the boot and watch for ingress (but we all know that's illegal - so maybe a camera?!).

If still no fix, i'll throw in the (wet) towel and give it it a local garage to fix.

Cheers
goose

 

[spartacus68]

Maybe not relevant - but I moved away from Sikaflex 291 and 292 to repair the panoramic sunroof on my B8. I noticed there was a technical bulletin for Volkswagen which used a foil in additional to this sealant. It's Henkel Teroson MS930. Touch wood, so far it's been dry. Sticks well to plastic and have no doubt it will work on metal. I ordered from RS Tools

Back to your predicament - I'd be inclined to remove Amp and use a little talcum powder and see if you get run marks to trace. I know it's messy - but you can remove one of the drain grommets and flush out afterwards.

 

[ninjag]

Would it be possible to create a ring of kitchen roll around the top of the boot well and then jet wash the car, so as to see if it's running down into the well from somewhere? If the kitchen roll is dry then presumably it would be coming from within the well itself so it would then just be a repeat with the roll in different places?

 

[Ant L]

I had a leak on my B8.5 saloon and the wheel well was filling with water. I took it to Audi and they changed the rubber seal around the boot and it stopped it.

 

[ninjag]

Just came across a post in another forum where it was mentioned that the rear wiper motor can leak into the boot.

 

[Simon]

It’s not something daft like the washer fluid line split is it? Would account for variable amounts

 

[g00se]

Just came across a post in another forum where it was mentioned that the rear wiper motor can leak into the boot.

Yes, this is a common failure point.. the rear washer nozzles get blocked over time, then fluid cannot pass though them and the motor in the tailgate burns out and leaks water inside the tail gate and it runs down into the boot/wheel well.

I have checked my rear nozzles and took the all the rear tailgate apart, and all was clear and dry in there... no corrosion or signs of screen wash.

The search continues...

goose

 

[RACK]

Did you ever find the cause of the leak goose?

 

[g00se]

Did you ever find the cause of the leak goose?

Hi Rack,

Well yes and no is the answer!!

A couple of weekends back i got the rear of the car up on ramps, took the wheel arch liners out, rear lights out, and rear bumper off... and basically sealed everything with clear silicone!

Rear lights openings, rear bumper vents, any rubber grommet (and there are many!!), the battery vent grommet.. inside and out.

I also needed a new battery this week (OEM was 10 yrs old) ans still had my suspicions it was the battery leaking.

But hey ho, multiple drives in the dry and wet, and zero leaks so far (fingers crossed). Will keep the carpet, B&O sub, spare wheel, boot floor, bootliner, dog bed, out for a while longer so i can monitor the situation... and may even leave out till after my next ring trip at the end of July.. as full disclosure, you can really notice the weight saving - that lot must be best part of 30-40kg!!!

Cheers!
goose