In my 'shop today, W176 with a pond inside...

Uncle Benz

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This is a very common problem. Manifests itself as a puddle in front and rear foot wells, most commonly on just one side of the car to start with. For quite a while Mercedes were fixing these for free, but that seems to be getting rarer now, and in fact a lot of cars are coming in for their second time. Air vents behind the rear bumper are the root cause of this fault. Mercedes have superseded the original part number, but to be honest I cannot see any difference in the part, so it will likely rear its ugly head again in time.
First step is rear bumper off...

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You can see the two vents just below the black bumper reinforcers. This is with the vents removed...

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This is the vent itself. You can see the yellow/cream soft rubber seal. This is the problem. It stops sealing and rainwater sneaks in between the body and the seal. From there it tracks along behind the inner arch trim and sluices down under the rear seat onto the floor.

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The design is not that clever. The rear lamp seals to the body with a triangular foam, and rainwater drains behind the body of the light itself, through the back of the bumper reinforcer and straight onto the yellow/cream seal of the vent.

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To fix the problem for the longer term I fit some new vents, but clean the mounting area thoroughly with some degreaser...

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And apply a bead of silicone sealer to the yellow/cream edge of the new vent...

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With the new vent clicked into place a satisfying splodge of silicone oozes around the edge. It matters not how it looks, because the bumper hides it all...

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All that's left to do is refit the bumper.
 
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Uncle Benz

Uncle Benz

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Some points to note if you fancy a go yourself. The hardest part is rear bumper removal. First off remove the rear lamps. They are held with a plastic wing-nut type affair...

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Then the centre plastic trim that covers the boot striker needs to come out. Remove the two luggage hooks, the centre bolt and then it levers up off of six plastic clips...

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With that out the way you can remove two grommets to reveal a couple of 10mm nuts run down very long guide pins. You need a rediculously deep socket, but I use a regular deep socket and a croc nose mole grip...

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Then you have four acme type bolts, one each side where the bumper meets the rear quarter panel, then yank the bumper outwards from plastic guide it sits in.

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And two underneath near the exhaust tailpipes...

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Six push pin rivets hold the arch liner to the bumper, three each side

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And then probably the trickiest bit. The bumper cover is clipped into the black bumper reinforcer each side, just below where the rear lamp fits. It needs teasing out. I have a nice wedge trim tool thing that does the trick...

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Don't forget to unplug the parktronic sensors if fitted. Lay out an old blanket for the bumper to save marking the paint.
 

Chrishazle

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Yet another "designed by an engineer" story - I lost track of the number of those I came across in my working life! Bit like a Renault model (not sure which) where I believe you have to remove the front bumper to replace a headlight bulb!
 

ajlsl600

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a "leading "car maker, cant keep unpressurized water out of its cars !! and knows the origin of the ingress !!, i would worry about what else "cant" be resolved.....
 

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a "leading "car maker, cant keep unpressurized water out of its cars !! and knows the origin of the ingress !!, i would worry about what else "cant" be resolved.....

They just gave up with the Smart Roadster & ended production after spending ££s on water ingress warranty work.
 

LostKiwi

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They just gave up with the Smart Roadster & ended production after spending ££s on water ingress warranty work.
Not strictly true.... Smart was losing bucket loads of money and had three separate product lines at the time. When they canned the roadster they also canned the For 4 in order to simplify the product range.
The water leaks in the roadster didn't help it's case as it made it a slow seller due to the reputation it gained but as we know the water leaks aren't that hard to fix.

I think one of the worst designs has to be land Rover. To remove a turbo on the TDV6 Discovery 3 requires the body to be lifted off the chassis (though some Indy's have found a way to avoid this).
 

Andy.M

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Great write up and descriptions, have a virtual pint!

Does this effect the GLA do you know?
 

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I couldn’t tell the difference with modified part either.
 

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They just gave up with the Smart Roadster & ended production after spending ££s on water ingress warranty work.
I was talking to a smart speacialist and was told my Fortwo convertibubble is much dryer than the hardtop... He explained they didn’t glue the roofs on the hardtops very well and they leak badly... never had a water leak in mine.
 

LostKiwi

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I was talking to a smart speacialist and was told my Fortwo convertibubble is much dryer than the hardtop... He explained they didn’t glue the roofs on the hardtops very well and they leak badly... never had a water leak in mine.
Strangely the Roadster with the softop is often drier than the optional removable hardtop (and quieter).
 

EmilysDad

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I was talking to a smart speacialist and was told my Fortwo convertibubble is much dryer than the hardtop... He explained they didn’t glue the roofs on the hardtops very well and they leak badly... never had a water leak in mine.

My Fortwo 451 has a clear-ish perspex roof. Though it didn't leak the roof on my car was loose on one corner. My fix was to lift it & squirt Tigerseal in the gap then clamp it down while it cured.
 

ajlsl600

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come on lads. we have active this active that ,headlights that see round corners and god knows wots coming, dont we think that keeping water out should be mastered first ?? and if we can do it with a bit of persistence and a tube of sealer wot are we to think of the makers .?? tho i have not had water in my R230 boot, does it not beggar belief that benz can ask 50/70 K and MORE for a car that often fills the boot with water wrecking a fortunes worth of expensive /complex electronics, this also happens in front footwells !! NOT impressed, even if on a 15k dacia duster and i have not read anywhere that it happens on them ???
 

EmilysDad

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It took me ages to work out why my tailgate was filling with water .... for whatever reason, Merc used ally for the captive nuts that holds a chrome trim on. The ally rotted & water found its way passed the trim.
 

ajlsl600

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It took me ages to work out why my tailgate was filling with water .... for whatever reason, Merc used ally for the captive nuts that holds a chrome trim on. The ally rotted & water found its way passed the trim.


bean counter worked out 10 cents a 1000 saving, also i have seen alli nuts that have no threads hole sized to allow threading as driven on!!! saving on nut threading....
 

Ken_R

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An interesting read. Thanks. An alternative to Silicone (which can go hard/brittle over time/temperature changes) is Butyl Rubber.

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Everflex 145 Butyl Rubber Sealant is a traditional permanently plastic one component sealant based on polybutene that provides an effective weatherproof seal in a variety of exterior and interior applications. 145 Butyl Sealant forms a skin in 24 hrs but remains permanently plastic underneath. The sealant accommodates joint movement of +/- 5%, is over paintable and exhibits good UV and chemical resistance.

My underscore emphasis. The difference being that if thermal changes breach the contact transition then exposure to air will cause this product to then again, naturally 'skin over'.

We use it in a number of applications. Many don't like it as, if you get it on your hands/fingers, it leaves a black residue which is difficult to remove for a couple of days. Any surplus on the work area can be removed using turps/thinners.

I am still down to Zero 'Smilies'! DOH!
 
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Uncle Benz

Uncle Benz

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An interesting read. Thanks. An alternative to Silicone (which can go hard/brittle over time/temperature changes) is Butyl Rubber.

145GY-60x350.png




My underscore emphasis. The difference being that if thermal changes breach the contact transition then exposure to air will cause this product to then again, naturally 'skin over'.

We use it in a number of applications. Many don't like it as, if you get it on your hands/fingers, it leaves a black residue which is difficult to remove for a couple of days. Any surplus on the work area can be removed using turps/thinners.

I am still down to Zero 'Smilies'! DOH!

I'll take a look at that, thanks! The main point was, Mercedes don't put anything on that joint.
 

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Uncle Benz

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To add something I failed to mention in the original post, one of the dead giveaways of this fault is visible condensation within the rear lamp. If you can see any condensation inside the top of the rear lamp from outside then you have water getting in through the body vent. Often you can see only one side affected, but if you are having the bumper off anyway you'd be foolish not to do both sides.
 
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Uncle Benz

Uncle Benz

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Could one of the mods maybe put this in the diy section? Now the search function seems poor I have personally referenced this thread a few times for enquiries. If it was in the diy section it might be found more easily.

If of course it is good enough ;)

I humbly request :)
 


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