A glass hydrometer with a balloon, a suction tube and an internal float, intended for measuring the filling of a cars radiator.

Glycol-based liquids as well as methanol-based coolants can be measured with this hydrometer.

The measurement of the liquid state is done by sucking the cooling liquid into the glass tube. By subtracting the values on the float, the temperature in degrees Celsius at which the measured liquid freezes can be determined.