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Thread: Water accumulation in convertible bodywork

  1. #1
    Join Date
    Mar 2020
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    BMW 420 Cabriolet

    Water accumulation in convertible bodywork

    Many people have reported hearing water sloshing around under the left hand rear window. This is due to a BMW design/assembly defect which BMW should be honest about and fix for free in all 4 series convertibles.

    Problem: The rear roof gutters and rear window seals drain into wells set in the bodywork under the rear windows. The right hand well connects by drain tube to the left hand well, which then drains via a 20mm drain tube which runs down to the underside of the bodywork on the left side, and discharges rainwater onto the road. At least that is the principle. In practice, BMW have failed to provide an outlet for this water! There are two black plastic liners fixed to the underside of the bodywork. These liners should each have a hole for water to pass out. In fact, there are no such holes, and the liners which are fixed below the tube outlet simply block any water from passing out.

    BMW claim in their technical service publications that the issue might be "dirt blocking the tube" but this is absolute hogwash. 20mm tubes don't get blocked by dirt. The issue is negligence in the design or manufacture of the liners - someone simply forgot to include outlet holes in the liners to let the water out.

    The solution is

    1. Get under the left side below the rear window and unscrew the first liner enough to ease it downwards. At this point, water may start pouring out - so be warned! Video: https://youtu.be/Y9QvyKqRc1I
    2. Ease off the second liner. Let all water drain out. Video: https://youtu.be/IWT0pEbMrtA
    3. Drill a 10-20mm hole through both liners immediately under the drain tube outlet. Refix the liners. The photo shows a 20mm hole I drilled, bit close to the edge,, but there will never be another blockage
    . thumbnail-38.jpeg

    Job done in 15 minutes. Should be done by BMW but fat chance of that. Shame on them.
    Last edited by Richard Bird; 03-09-2020 at 05:14 PM.

  2. #2
    Join Date
    Sep 2006
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    https://www.bimmerforums.com/forum/s...onvertible-F33


    Check out Post #9. BMW already has a fix for this. But no, they're not going to pay for it.

    I think the problem isn't that the 20mm hole itself is getting clogged with dirt, it's that there's only 2mm between the sheet metal with the drain hole, and the plastic side skirt that doesn't have a hole, so that's why dirt accumulates and blocks the hole. And also why they tell you to drill a hole in the plastic piece.
    Last edited by Critter7r; 03-09-2020 at 03:38 PM.
    Quote Originally Posted by B4SH View Post
    If anyone knows, it's this guy who knows literally nothing about everything.
    Quote Originally Posted by fcvapor05 View Post
    Do you even OT? The mean 401k around here is probably about $6, what with all the shiny cars and $1,000 watches and donations to get other members' Volvos running.


  3. #3
    Join Date
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    Dirt is not the issue. It is that the cover plates (both plastic) totally block the drain tube outlet. No hole in either plate! Design or manufacture error which BMW try to blame on the user for allowing 'dirt' in. Hogwash.
    Last edited by Richard Bird; 03-09-2020 at 05:23 PM.

  4. #4
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    Either way, the fix is to drill a hole.
    Quote Originally Posted by B4SH View Post
    If anyone knows, it's this guy who knows literally nothing about everything.
    Quote Originally Posted by fcvapor05 View Post
    Do you even OT? The mean 401k around here is probably about $6, what with all the shiny cars and $1,000 watches and donations to get other members' Volvos running.


  5. #5
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    All of us at my shop are also removing the spiral plastic drain blocking thingy. We have seen them totally clogged with dirt and debris.
    ASE and BMW Master Certified Technician

  6. #6
    Join Date
    Aug 2012
    Location
    Bucharest, Romania
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    bmw 318i
    Hello.

    I am having the same issue with this. I got to access the drain hole, and it was clogged. I jiggled it a bit, and water came out, but I cannot remove it entirely.

    How do you remote the drain plug?

    Thanks.

  7. #7
    Join Date
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    I assume a pair of pliers or a drill would do the trick. (I've never done one, I just see the procedures that BMW provides).

    But check this thread ..

    https://www.bimmerforums.com/forum/s...onvertible-F33
    Quote Originally Posted by B4SH View Post
    If anyone knows, it's this guy who knows literally nothing about everything.
    Quote Originally Posted by fcvapor05 View Post
    Do you even OT? The mean 401k around here is probably about $6, what with all the shiny cars and $1,000 watches and donations to get other members' Volvos running.


  8. #8
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    It's a 14 mm allen, if you have one that size (same size that fits differential drain/fill plugs). It's a 1/4 turn I think, then it will pull out.
    ASE and BMW Master Certified Technician

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