Polarization resistance (PR) and corrosion behavior diagram (CBD) measurements are described which provide a rapid means of determining the effectiveness of inhibitors for aluminum corrosion in automotive coolants. The polarization resistance measurement gives a direct measure of the general corrosion rate of aluminum. The area of the hysteresis loop in the CBD is shown to be very sensitive to the degree of pitting of aluminum in a given coolant environment. The combined PR and CBD measurements take about 40 min to perform.