Today I got the message the coolant level is low, checked when cold, it was below the minimum. I made the mistake of partially opening the coolant cap while engine temp was halfway to its operating temp. I heard a sound of pressurized air (sucked in or pumped out) so I closed it back.

Now I can hear sound of liquid moving (air bubble?) every 3-5 seconds, but only while the ventilation is turned on.

What should I do? Thank you.

  • Welcome to Motor Vehicle Maintenance & Repair! What is the year/make/model/engine of the vehicle in question? Nov 17, 2018 at 13:45
  • Hi. It's a 2012 BMW 5 series, diesel, which uses G11 coolant.
    – CristianC
    Nov 17, 2018 at 13:46
  • This has a coolant recovery tank on it, correct? Nov 17, 2018 at 13:52
  • It's a small plastic reservoir with a cap. Inside it there's a min and max mark.
    – CristianC
    Nov 17, 2018 at 13:53
  • How many hoses are attached to it? Nov 17, 2018 at 13:57

1 Answer 1


Your coolant system may be a bit low, but shouldn't be an issue. Just pop the top when the engine is cold and fill until it gets to the desired height. If it's a bit low, there may be air in the system causing the noise. Your system, having a recovery tank (versus an overflow) circulates coolant through it while running, which means the cooling system is self bleeding. Just fill the coolant up and run it like normal. Double check it the next day to ensure it's still good.

As an aside, there may be a reason your coolant is a bit low. You'll want to keep your eye on the levels and if it gets low again, consider taking it to a mechanic and let them know you are losing coolant. There may be a slow leak, which could exhibit itself on your garage floor or through the smell of antifreeze when running. Pay attention to the levels for the next while to be sure.

  • I haven't changed the coolant since I bought the car two years ago, now it's the first time I got the message and only once. I am concerned with the gurgling sound that I can hear now since opening the cap the 2nd time (while engine was getting warm).
    – CristianC
    Nov 17, 2018 at 14:07

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