Low coolant light won't go off

[rlubocki]

I have a 2004 Z4 3.0i, and last week my low coolant light went on. I checked the coolant reservoir while cold, and yes it was low. I added the recommended amount, and the light is still on! I do not see any evidence of a leak, and cleaned all the flooring below the radiator and the reservoir, so its dry. Engine temp is normal... Any ideas?
Love my car, but when this happens it spoils everything...

[Blind32]

Did the red bobber float up when you filled it up? I remember working on my buddies 5 series and the red bobber had gotten stuck in the down position and even though it had fluid, the light was still on. We had to tap the reservoir to make it pop up.

[seank]

WHS, not coming up or the sensor is bad at the bottom of the expansion tank.

[StickMon]

Did you check it again after the initial fill?
If the tank went empty the level in the system would be low.
It'll suck more out of the tank when you run it.

[rlubocki]

Originally Posted by StickMon

Did you check it again after the initial fill?
If the tank went empty the level in the system would be low.
It'll suck more out of the tank when you run it.

That is a good point!! I will check that out, perhaps when I ran the car and it sucked more fluid into the system I need to add more to top it off. I never checked after toping off the tank, maybe it needs more. Thank you for great advice!!

[rlubocki]

The bobber did come up when filling it up, and it was leveled at recommended marking. Thank you for advice, keep them coming!

[seank]

Bad sensor

[v8z4]

The low-coolant-sensor is just a reed switch that is normally closed (power can flow) and opens in the presence of a magnet (low coolant lets the magnet "fall" and open the switch).

I just got done building an aluminum reservoir and because my tank does not have the sensor, I just wired in a 1ohm resistor to turn the light off for good.

[rlubocki]

Great advice, thank you!! Can you get a sensor, or I need a whole tank unit?

[v8z4]

Should be able to buy a sensor separately since it is removable (it twists out). Before you go buy a new sensor, test the sensor. Pull the current sensor out of the tank (comes out from the bottom) and see if the light goes off. If it does, the the sensor is not bad. If it doesn't, then unplug the sensor and bridge the contacts on the plug (like I mentioned above). If the light goes off, the sensor is bad.

[Shipkiller]

Are you sure you vented the system properly?

http://www.shipkiller.com/Venting_Co...System_M54.pdf

[rlubocki]

I am actually testing the sensor right now, and the level of the coolant after topping it off after 2 days. will let you know. I appreciate your advice!!!