Coolant light will not go out
 

1987 300D The light flickered occasionally for several days but went out fairly quickly. Today it came on and stayed on. Topped off the coolant reservoir. Temp is normal. No apparent leaks. Ideas?

Something's wrong with the sensor on the overflow tank. You need to try pulling it out and cleaning it or simply unplug it if it bothers you.

Coolant light
 

I hate to answer my own post but I seem to recall something about how getting low on windshield cleaner can cause the coolant light to stay on. I will try in the morning.

I believe they are different idiot lights. IIRC they look similar so it may be that your low washer fluid light is the one that is on. If not I would agree that the sensor has gone south.

The sensor is most likely just like the one on a 3 series BMW (a reed relay switch activated by a magnet when the level is proper)

Take the sensor out, clean it all up, check it out. Check the wiring and make sure its all solid. The antifreeze doesn't do much for the wiring (sorta hard on it) so check it over real good.

Also check to make sure ALL your fluids are topped up :)

Yep, they are different lights. My washer fluid light stayed on all the time even when the tank was full. I remember reading about the float switch will only work with the Mercedes brand washer fluid. I assume it is more dense than normal washer fluid. I just unplugged my sensor and problem solved-I don't need an idiot light to tell me when the washer fluid is getting low.

It worked
 

As I speculated earlier in this thread, I thought that I remembered that a low windshield wiper fluid reservoir might be the cause of my coolant light being on constantly. I thought that I remembered that one from the days when I took the car to a dealer for service. I paid for many of those sensors and eventually a tech told me that it was low windhshield fluid.

I filled it today and the light went out instantly. So those of you who have disconnected the sensor might want to try hooking it back up and filling the wiper fluid tank.