The increasing use of aluminum for engine and cooling system component design has resulted in the need for improved monitoring of cooling system performance. These new systems are more susceptible to damage from corrosion and overheating. A sensor is now available that responds to inhibitor depletion and to low coolant level in service. This device combines sensing electrodes and electronics into a package that mounts directly onto the radiator and provides a compatible vehicle computer output. This paper describes the design, application, and performance of this sensor.