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Thread: Coolant reservoir cap stuck

  1. #1
    Join Date
    Mar 2011
    Location
    Hawaii
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    152
    My Cars
    635csi, 330ci

    Coolant reservoir cap stuck

    Trying to get my 6 back in shape, along with dealing with power steering noise, had the coolant warning light come on. Went to top off the coolant but the coolant cap is stuck. I can turn it the quarter turn to release the tabs, but it won't come off. Searched but didn't find any threads for an e24. I'm hesitant to force or pry it off, I don't want to damage the reservoir. Has anyone run into this issue that can offfer some advice on what to do, or what not to do? I didn't want to force the cap, unplugged the coolant level sensor and unscrewed the plastic nut it's in and filled the coolant through that hole. Coolant light on the control panel went off but came back on a few minutes later, maybe the level sensor is no good, maybe the connector.
    The car is a '89 635, 33,xxx miles, has been sitting for most of its life for years at a time. Honestly the last time the cap was opened was likely over a decade ago, maybe even 15 years. I got it from the previous owner about 8 years or so ago, it's mostly sat under my ownership as well. Very likely with the exception of the oil filter everything under the hood is factory original.
    Appreciate any tips or experience anyone can throw my way.

  2. #2
    Join Date
    Apr 2005
    Location
    Savannah GA
    Posts
    651
    My Cars
    '73 ///M2, '85 ///M635
    Well, I'd spray some WD-40 or similar under it.

    Good luck,

    Ray

  3. #3
    Join Date
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    Delicately, with a rubber mallet.

  4. #4
    Join Date
    Aug 2010
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    West Nyack, New York
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    86 635csi 98 740i 96 MB
    Push down on cap while twisting. I've had my 6 for 30 years and the cap has always been a tough one,
    even with a new overflow and new cap.

  5. #5
    Join Date
    Apr 2008
    Location
    Scottsdale, Arizona
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    4,885
    My Cars
    81 euro 635, 4.4 X5
    Quote Originally Posted by 1986series6 View Post
    Push down on cap while twisting. I've had my 6 for 30 years and the cap has always been a tough one,
    even with a new overflow and new cap.
    +1 Had this same issue yesterday and it took a lot of downward pressure to get the cap to turn all of the way
    81 Euro undergoing total nut and bolt restoration
    pictures at: flickr.com/photos/bertsphotos

  6. #6
    Join Date
    Mar 2011
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    Hawaii
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    152
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    635csi, 330ci
    Quote Originally Posted by MIKYZZ4 View Post
    Delicately, with a rubber mallet.
    ����
    Quote Originally Posted by 1986series6 View Post
    Push down on cap while twisting. I've had my 6 for 30 years and the cap has always been a tough one,
    even with a new overflow and new cap.
    Quote Originally Posted by rlkrlk View Post
    Well, I'd spray some WD-40 or similar under it.

    Good luck,

    Ray
    Quote Originally Posted by Bert Poliakoff View Post
    +1 Had this same issue yesterday and it took a lot of downward pressure to get the cap to turn all of the way
    Ill give it that technique a try. Thanks guys!

  7. #7
    Join Date
    Dec 2022
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    Nebraska
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    '16 340i xdrive
    Quote Originally Posted by MIKYZZ4 View Post
    Delicately, with a rubber mallet.
    MIKYZZ4, I want to thank you for this simple reply which solved my problem! I'm female, 100 pounds and the cap was way beyond my strength level. Gentle rubber mallet taps worked like a charm! Thank you!

  8. #8
    Join Date
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    EXOTICS
    Glad i was able to solve this so easily.

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