Low coolant warning, but it's full

Discussion in 'General Motoring' started by Doug Miller, Apr 4, 2011.

  1. Doug Miller

    Doug Miller Guest

    99 SL2, 130,000 miles. A week ago, the upper radiator hose burst. I drained
    the cooling system, replaced both hoses, and refilled the system. Two or three
    days later, the low coolant warning began flashing. Checked the coolant level
    -- sure enough, it's low. Topped it off (about a pint). Two days later, the
    warning is *still* flashing, even though the system is filled all the way to
    the "Max Cold" mark on the tank. What gives?

    One more oddity: the low-coolant warning did *not* flash when the hose burst,
    despite dumping about half of the system on the street.
    Doug Miller, Apr 4, 2011
  2. Doug Miller

    Oppie Guest

    I had to replace the coolant tank in the '01 lw300 last year because of a
    broken float switch. The float caries a magnet that actuates the fixed reed
    switch in the tank. Been fine since.

    You might have had to add fluid because all the air was not purged from the
    high points of the system. Eventually the air works its way out and the
    fluid level will accordingly drop. In cases where there is still trapped
    air, the coolant level may drop as pressure increases... causing a low
    coolant level.

    Given your last entry about the low coolant warning did not flash... I would
    strongly suspect the coolant level float switch is stuck, as was mine.

    btw- disconnecting the float switch will turn the indicator ON.
    Oppie, Apr 5, 2011
  3. Doug Miller

    Doug Miller Guest

    Right, I'm sure that's why it dropped after the repair.
    Ahhh, hadn't thought about that. After a week, though -- including a weekend
    trip out of state -- I would think that any trapped air should have worked its
    way back to the tank by now. I've driven the car about 300 miles since topping
    off the tank, and about 400 since the repair.
    Is there any way to free a stuck switch? Or do I have to replace the tank?
    Hmmm... I guess that's another thing to check: if the connector somehow came
    Doug Miller, Apr 5, 2011
  4. Doug Miller

    Oppie Guest

    I have a buddy with a repair shop that gets me parts at his cost. Tank for
    the lw300 cost me $65. Can't say for sure on your car but the switches are
    generally molded into the tank and can not be replaced separately.
    Oppie, Apr 5, 2011
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