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Thread: Low Coolant light on all the time

  1. #1
    Join Date
    Jun 2011
    Location
    Hanover,PA
    Posts
    15
    My Cars
    2004 325I

    Low Coolant light on all the time

    I replaced my thermostat and Expansion Tank on my
    2004 330XI. There are no leaks and the coolant is full.
    When I start her up the low coolant light just comes on and
    stays on. I have read online that this could be a bad
    Low Coolant Sensor. But I did replace that when I
    replaced the Tank. It was not a BMW brand.
    Someone also suggested I plug the old sensor into
    the lead and turn it upside down. Light still on.
    I have drained the system 4 times through all
    this. If the new sensor is not working I guess the only
    way to know for sure is to once again drain the
    system and try a better sensor? Or am I missing
    something? Help!

  2. #2
    Join Date
    Jul 2011
    Location
    Arlington, VA
    Posts
    9,931
    My Cars
    2018 BMW M240i
    This sensor is a very simple device. It’s basically 2 thin pieces of metal that are just barely separated. The red tank level bar has a magnet in its base. When the level is low the magnet surrounds the 2 thin pieces of metal, and the magnetic field forces them together. That lights the warning light in the dash.

    One of the “rules” that I follow is to never install an aftermarket sensor of any kind in my bimmwe. This is no exception. I’d reinstall the old sensor and see what happens. Now, if the light still comes on then there’s a wiring short somewhere.

  3. #3
    Join Date
    Nov 2016
    Location
    Charlotte, NC
    Posts
    1,534
    My Cars
    '02 540i-6, '97 540i-6
    The problem might be in the wiring or the plug connection. Check those too.

  4. #4
    Join Date
    Jan 2016
    Location
    Ca
    Posts
    6,981
    My Cars
    2001 525it
    We had issues with e36 after market sensors the pin size was wrong so it wasn't making a good connection

  5. #5
    Join Date
    Sep 2006
    Location
    Michigan
    Posts
    13,674
    My Cars
    2005 325Xi
    Aftermarket tanks sometimes cause problems too.
    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.


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