An electrochemical test based on the measurement of galvanic currents has been developed for water-glycol solutions on five different metallic materials. An acidity function is first defined for ethylene glycol, propylene glycol, and water glycols, which allows comparisons to be made of their aggressiveness towards metals. Different combinations of inhibitors are tested by using the method. It is shown that the method is particularly suitable for testing aluminum: the effects of inhibitors on the behavior of the oxide layer, on pitting tendency, and on general dissolution of the metal are easily detected. The corrosion parameters may be continuously monitored by inserting the electrochemical cell into the cooling system of a car.