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Thread: RPM's dropping while cruising and bipolar coolant level light help

  1. #1
    Join Date
    Jun 2016
    Location
    Seattle
    Posts
    13
    My Cars
    99 540iA (sold)

    RPM's dropping while cruising and bipolar coolant level light help

    Bimmerforum users,

    I drive a 99 540iA with 152k. I have two problems; When driving at a constant speed, say 60mph, I'll be at the same RPM's and then it takes about 5 seconds for my car to drop about 250 lower, then it will spike back up to where it was, then 5 seconds later im back down 250 lower, and this occurs literally 100% of the time. I've read it could possibly be a torque converter but that was the only other thing on the internet concerning this I could find (for E39's anyway).

    Second problem; I got my first coolant level low light 5 days ago. I checked and it was very low almost empty. I grabbed my coolant and went to refill it, however I was no more than 2 seconds into pouring my coolant in when the needle floated up immediately and was all the way full. Fast forward to today, I go to turn my car on and I get the light on again. I check it, immediately after removing the cap, pressure is released and my needle starts to float all the way up to full. Also, there is coolant coming out of the top part of the expansion tank or from the cap.

    Any idea what would be causing these problems?

  2. #2
    Join Date
    Oct 2010
    Location
    San Jose, CA
    Posts
    11,537
    My Cars
    1997 BMW 540i 6 speed
    Sounds like the lockup clutch (or solenoid) is malfunctioning. Get the trans codes read.

    Coolant must always be checked with a cold engine. The float s/b level with the top of the hole.


    Ed in San Jose '97 540i 6 speed aspensilber over aubergine leather. Build date 3/97. Golden Gate Chapter BMW CCA Nr 62319.

  3. #3
    Join Date
    Jul 2016
    Location
    Chicago, Illinois
    Posts
    3,842
    My Cars
    are slow
    Expansion tank sensor might be going, get a new tank.

    Some people with E38s solved it with a fu trans fluid changd.

  4. #4
    Join Date
    Jun 2016
    Location
    Seattle
    Posts
    13
    My Cars
    99 540iA (sold)
    Air is in my cooling system, gonna bleed it tonight and update if the problem persists.

    As for the waining RPM's, I have found the holy grail thread with 25+ users experiencing the same problem. Might have to fork out $83 per ignition coil to fix it... or I can just live with it

  5. #5
    Join Date
    Oct 2017
    Location
    Atlanta, GA
    Posts
    9
    My Cars
    2003 525i
    Quote Originally Posted by PNW540i View Post
    Air is in my cooling system, gonna bleed it tonight and update if the problem persists.

    As for the waining RPM's, I have found the holy grail thread with 25+ users experiencing the same problem. Might have to fork out $83 per ignition coil to fix it... or I can just live with it

    Need help in finding the "holy grail" thread noted above. I have the same issue, 2003 525i automatic with 105k. Just had trans fluid and filter changed and still have the issue. I assume based on the comment above the coils need replaced to resolve?

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