I have been testing this breadboard of a coolant level alarm and it works great. The sensor is from a VW. As you can see, when in contact with the coolant, it is silent. When not in contact, the piezo buzzer sounds.

I believe the VW type sensor will be much more reliable than the float/reed switch level sensor on the W126 coolant expansion tanks. Mine has a buzzer which you can't miss and will nag you till you correct the coolant level.


CLICK TO PLAY!

__________________
85 300D turbo pristine w 157k when purchased 167,870 July 2025
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

Thanks to Jooseppi Luna for the W123 expansion tank. 2 stainless screws will serve as the probe.

__________________
85 300D turbo pristine w 157k when purchased 167,870 July 2025
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

Bench testing the probe in the expansion tank. Tilting the tank such that the coolant in not in contact with the probes, the buzzer sounds. I will be installing the tank into my 85 300D for field testing once I put the circuit into a pill bottle.

Will report back in a few weeks on how it's doing.


CLICK TO PLAY!

__________________
85 300D turbo pristine w 157k when purchased 167,870 July 2025
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked