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Thread: failed expansion tank cap

  1. #1
    Join Date
    Jul 2011
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    hillsborough n j
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    2001 540i sport 6spd

    failed expansion tank cap

    a few weeks ago i noticed that there was a large o-ring down inside my expansion tank so i fished it out. turns out it fell of the cap. upon closer inspection the cap as been chewed off at the bottom.



    notice how flattened the o-ring is to the plastic ring width = bad



    the last ring is all broken apart so there was nothing left to hold the lower o-ring.

    i also had some slight coolant crispies inside the bottom of the cap lid.
    the cap is designed so that the part with the o-rings rotates freely from the lid so you can screw the lid onto the tank without the o-rings being dragged against the inside of the tank neck.

    this is what the new one looks like so you can see how much broke off.

    the o-rings here are much puffier for a better contact seal.




    the outter ring with the writing on it was missing.




    i suspect the car's previous owner to have attempted the fabled
    "beaver chewed expansion tank cap to lower the bar pressure mod"
    Last edited by topaz540i; 01-22-2012 at 08:56 PM. Reason: Automerged Doublepost
    ~2001 540i/6speed~
    Schmiedman M5 headers, SPEC stage2+ kevlar clutch, JBR 11lb lightweight flywheel, ESS Tuning m60 manifold software tune, 3" SS freeflow OBX catback, afe cold air intake, m60 intake manifold, Cdv delete, powerflex urethane sway bar bushings, M5 rear sway bar ,Autozone replacement driver side blinker light bulb, 545 short shifter zhp weighted, "dsc off" sticker, m5 3.15 lsd differential, m5 chassis rods, akebono ceramic pads, G2 caliper epoxy, ecs braided lines, BC-Racing br-plus series w/swift springs 8/6~
    On the night that I go back in time, you will be shot by terrorists. Please take whatever precautions are necessary to prevent this terrible disaster.

  2. #2
    Join Date
    Sep 2009
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    Toronto, Canada
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    02 BMW 540i, Volvo XC90
    Try not to over tighten it, let the o ring to the job.

  3. #3
    Join Date
    May 2011
    Location
    O'Fallon, IL
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    1998 540i
    LOL @ beaver joke

  4. #4
    Join Date
    Sep 2006
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    New York
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    2003 525i
    I replace mine every two years. Or less. It's ten bucks and well you know the rest when it comes to our uncool, cooling system.
    "I'd smash that (Jennifer Connelly) like a failed coup in sub-Saharan Africa."
    ~Macktheknife in my epic Jennifer Connelly OT Thread

  5. #5
    Join Date
    May 2007
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    Cowtown -The Great NW
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    2003 530iA
    Every two years is overkill.
    Every time you overhaul the cooling sounds right.
    I overhauled the cooling sytem and the only thing I didn't change is the expansion tank cap. I think I will change it now.

    That thing you had looked gross...
    Looking for a DIY? Parts? Check this out, it might be your ticket

    Stable: e92is, e53 N62, e46M54B25, Tribby & e39 M54B30 R.I.P.

  6. #6
    Join Date
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    2001 540i sport 6spd
    it wasnt all grimy. it was just really shiny with fresh coolant the way the plastic chipped off all rugged.

    to see if you cap is still good look at my before and after o-ring pics.

    also check for fried coolant on the inside of the cap.
    ~2001 540i/6speed~
    Schmiedman M5 headers, SPEC stage2+ kevlar clutch, JBR 11lb lightweight flywheel, ESS Tuning m60 manifold software tune, 3" SS freeflow OBX catback, afe cold air intake, m60 intake manifold, Cdv delete, powerflex urethane sway bar bushings, M5 rear sway bar ,Autozone replacement driver side blinker light bulb, 545 short shifter zhp weighted, "dsc off" sticker, m5 3.15 lsd differential, m5 chassis rods, akebono ceramic pads, G2 caliper epoxy, ecs braided lines, BC-Racing br-plus series w/swift springs 8/6~
    On the night that I go back in time, you will be shot by terrorists. Please take whatever precautions are necessary to prevent this terrible disaster.

  7. #7
    Join Date
    Sep 2006
    Location
    New York
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    5,563
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    2003 525i
    Quote Originally Posted by Doru View Post
    Every two years is overkill.
    Every time you overhaul the cooling sounds right.
    I stated as much. But this is not the only coolant-cap thread. It's ten dollars, maybe $8.00 if you know where to buy it. That's lunch money. I replace my coolant every two years. I replace the drain plug and o-ring each time. I place a new cap on the tank every time.

    topaz, good u found it before something occured.
    "I'd smash that (Jennifer Connelly) like a failed coup in sub-Saharan Africa."
    ~Macktheknife in my epic Jennifer Connelly OT Thread

  8. #8
    Join Date
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    2001 530i (E39) 128k
    Quote Originally Posted by bimmerfiver View Post
    It's ten dollars, maybe $8.00 if you know where to buy it. .
    ...and if you don't know where to buy it, try my website:
    http://furiousmethod.com/
    and type in part number 17111742231

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