E39 coolant level sensor

[NC540i]

I have a 2000 540i and am having a problem with the coolant level sensor. The other day I checked the coolant level and didn't tighten the rad cap all the way. I drove a short distance and the coolant level sensor chimed. I went home and noted the cap not being tight and a little coolant streaming out. I let the engine cool and checked the level and added some coolant (tightened cap all the way). I have driven several times and the coolant level sensor keep coming on after about 1-2 minutes of driving. I keep checking the level and it's OK.

Has anyone experienced a similar issue with the coolant level sensor? If it's the sensor why does it take a couple minutes to chime? ghead

[sp0rky]

My coolant level sensor has been telling me to check my level on my e34 ever since i had a coolant leak. I then repaired the leak, flushed and refilled teh coolant... it's been months and almost everyday, either on startup or in the middle of a drive - sometimes even at shutdown, itll tell me to check the level, and its been perfect ever since. I believe its just the sensor.. but im not sure

sorry if this didnt make sense, im typing in a hurry.

[NC540i]

Thanks, It does make sense. It may be that the sensor is malfunctioning. But, it's still annoying.

[sp0rky]

Yeah, its very annoying... I'm sorry that I was in a hurry earlier, I didn't get to finish my post.

My point was that maybe, just MAYBE the sensors have a tendancy to go bad once the fluid has dipped a little too low? Maybe someone who has more experience with these little thingers could tell us. By the way, if you want to get one for cheap: check ebay!

[NC540i]

OK, update time. My problem has been solved by reading a thread on another board. To check to see of the coolant sensor is working, 1) remove the rad cap and start the car, 2) push the float in the expansion tank down for at least 20 seconds and check inside the car to see if the sensor indicator is showing in the display, 3) pull the float up and hold for at least 20 seconds and check inside the car, the "check coolant level" display should be off. If both are working then your sensor should be OK.

My sensor is OK. The next thing to do is to observe the float while the car is running. I started the car with the rad cap off and observed the float drop so low that I couldn't even see it after bout 5 minutes. While the car was running, I added some 50/50 phosphate free coolant just until the sensor kicked off. I added coolant while someone in the car observed the display inside the car. I replaced the cap and drove the car for about 30 minutes (joy) and did not have the sensor warning. I think this will work out fine. I'll recheck the coolant level in the morning when the car has cooled and report results. If the coolant level has dropped overnight there is probably a leak.

I was also told that since I had not tightened the cap that air may have built up in the rad. So I blead off the excess air after I had driven the car. The bleed-off screw is right below the expansion tank cap, it's a phillips screw.