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Thread: coolant level sensor

  1. #1
    Join Date
    Feb 2004
    Location
    arkansas
    Posts
    39

    Default coolant level sensor

    Is there a way that you can test the sensor to see if it is working... My radiator is full and sometimes it says that I need coolant and sometimes it doesnt say anything... I took it apart and there was some weird brown stuff inside. I cleaned it out and put it back together.

  2. #2
    Join Date
    Mar 2006
    Location
    Derbyshire, UK
    Posts
    872

    Default

    The sensor is easily tested. It contains a magnetic reed switch actuated by a washer-shaped magnet on the float. Test for conductivity across the pins -- with the float in one position, the switch should be open; with the float in the other position, the switch should be closed. The weird brown stuff inside the sensor is probably rust and water, especially if (as sometimes happens) the sensor wiring has been rusting away internally.

    1997 535i V8
    5spd, OBC, A/C, cruise, BMW phone, factory M-Tech wheel & suspension, 18" Alpinas

  3. #3
    Join Date
    Mar 2005
    Location
    Long Beach, CA
    Posts
    2,563

    Default

    These are notorious for acting up.

    Ralph Mendoza Jr. - Long Beach, CA

  4. #4
    Join Date
    Jul 2006
    Location
    Albany, NY
    Posts
    451

    Default

    Thanks for the info Dave. Do you have to drain the coolant to test/replace the sensor? It's only a $20 part, might as well just throw a new one in if your getting messages.

  5. #5
    Join Date
    Mar 2006
    Location
    Derbyshire, UK
    Posts
    872

    Default

    If the sensor is on the bottom of the radiator-mounted expansion tank (520i/525i) you need to drain the rad and it's much easier if you remove it and change the sensor on the bench.

    With the firewall-mounted expansion tank (535i/540i), draining isn't necessary.

    1997 535i V8
    5spd, OBC, A/C, cruise, BMW phone, factory M-Tech wheel & suspension, 18" Alpinas

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