A method for estimating a volume of thawed liquid in a motor vehicle tank, wherein the following operations are executed at regular time intervals: obtaining a temperature of the ambient air outside the tank using a thermometer; determining, according to said temperature outside the tank and by a first pre-established relation, a thermal energy transfer between the contents of the tank and the outside environment; determining, as a function of the power produced by a heating element, and by a second pre-established relation, a thermal energy transfer between the heating element and the contents of the tank; determining, as a function of the energy transfers, and by a third pre-established relation, an amount of thawed or refrozen liquid, during said time interval; the amounts of thawed and refrozen liquid are added during the preceding consecutive time intervals to estimate a volume of thawed liquid present in the tank.