Constant "coolant low" dash light

[X3456]

Replaced the expansion tank.
Bled and filled tank with coolant.
Coolant light still on after 2 days on the floor ramps...angeling the front of the car upwards.
Low coolant light still remains.
Took the car m54 out on the highway for a 4hour run .
Came back home, let the engine cool... removed the cap and float was just a bit under the mouth of the tank . Coolant light still remains. Added a little coolant to bring the float a inch above the mouth... can't overfill these things. We'll see in the morning if the light/warning still remains...
Any explanation to this?

[MarcoZandrini]

The tank has a switch in the bottom, as you know. I’d check the wiring for issues such as wires shorted together. What brand of tank did you install?

[Honolulu]

Coolant level sensor IIRC is the same as used in the windshield washer tank, and a common failure item. Plenty Youtube videos about this job. Jack up the front of the car, put on blocks or stands. Remove engine tray if present. CLS is at the bottom of the expansion tank, visible from underneath. Disconnect 2-wire plug, turn 1/4 to remove/replace. You'll lose some coolant when you take it out, so protect your eyes and face and DO NOT r&r while the coolant is hot. Have the new one ready to go in.

[X3456]

The tank has a switch in the bottom, as you know. I’d check the wiring for issues such as wires shorted together. What brand of tank did you install?

Yeah, the tank is aftermarket. The level sensor is the same one used previously on the original tank...no problems then.
I have several sensors on the shelf...its the older version. I have one where the wiring is enclosed by a tube...should that be removed? That is... the tube?

[X3456]

Coolant level sensor IIRC is the same as used in the windshield washer tank, and a common failure item. Plenty Youtube videos about this job. Jack up the front of the car, put on blocks or stands. Remove engine tray if present. CLS is at the bottom of the expansion tank, visible from underneath. Disconnect 2-wire plug, turn 1/4 to remove/replace. You'll lose some coolant when you take it out, so protect your eyes and face and DO NOT r&r while the coolant is hot. Have the new one ready to go in.

Thanks for the reply. I understand totally. Hate to loose the coolant. Hate to redo the job. I'm just glad it's not overheating. The problem must be in the sensor. So many other jobs to address. Think ill hold off for now. Maybe it will correct itself...doubt it tho. Ride for now and revisit later. After all it is a "Beater Beemer" it'll get me around town for now and give the other car a rest.
Thanks again! Everyone.

[MarcoZandrini]

You won’t lose any coolant when you swap sensors.

[X3456]

You won’t lose any coolant when you swap sensors.

Are saying when I untab the sensor and pull down I won't get a flood of coolant to the floor.

[MarcoZandrini]

In OE ranks the sensor is in a cavity in the bottom of the tank. Removing it doesn’t lose any coolant. What brand of tank did you install?

[X3456]

Thanks I'll just switch out the sensor and see if it cancels out the dash warning light.

[X3456]

Switched out the sensor... reassembled everything. Fired the engine up...low coolant light never appeared. I do remember the aftermarket tank was accompanied by these sensors... (bought 3) see pic. Don't know what the major difference is from OEM. Oh! And I didn't loose a drop of coolant

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[MarcoZandrini]

The installation of aftermarket cooling system parts is strictly verboten.

[E39 Newbie]

^^^ This!!

[X3456]

Thanks! I'll keep you posted...

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[X3456]

Middle of June now...All is well!