Low coolant warning light but it's full

[Doug Miller]

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.

 

[Oppie]

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.

 

[Doug Miller]

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.

Right, I'm sure that's why it dropped after the repair.

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.

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.

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.

Is there any way to free a stuck switch? Or do I have to replace the tank?

btw- disconnecting the float switch will turn the indicator ON.

Hmmm... I guess that's another thing to check: if the connector somehow came
loose.

 

[Oppie]

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.