A method and measuring device intended for a window-cleaning system of a motor vehicle, wherein the freezing temperature is determined by continuous cooling of a representative partial volume of the liquid inside a chamber. For this purpose, measurements are made of the temperature while the liquid is cooled, which first drops in accordance with the heat dissipation until the start of the phase change initiating the freezing, and in the process leads the heat of solidification released to a temporary temperature plateau. The freezing temperature can be reliably determined in this way for each chemical composition of the liquid.