Coolant indicator...
 

I recently replaced an upper radiator hose in my SDL because it sprung a major leak. I've topped off the coolant to the V-mark on the overflow reservoir. Even with the full level the coolant indicator comes on while driving. Another thing: when the engine is running (hot) the overflow tank seems about 3-4 inches lower than when the engine is off - is that normal?! Just don't understand why that indicator is coming on when the fluid level is at max. I should also mention that I've never had that indicator come on until the leak started it all... the indicator helped me find that there is a leak.

Clean the contacts in the reservoir fluid level sensor connector.

Did you bleed the system when you refilled after replacing the upper hose? If not, there was likely air in the system after you topped the reservoir, and the level dropped as coolant circulated.

Sixto
87 300D

How do you bleed the system?! I just topped of. Do you mean drain and re-fill the whole system with new coolant?

The system should bleed itself by driving with the heater set on full. Seems to take several iterations. To fill a system that's empty or particularly low, some folks fill through the upper hose. I remove one of the temp sensors on the engine side upper hose fitting and fill through the reservoir.

Sixto
87 300D