Low-freezing coolants for automotive engines are analyzed before and after oxidation. It is shown that ion chromatography can be used to monitor the composition change of ethylene-glycol-based coolants and to formulate recommendations for optimizing the method based on current specifications for automotive engine performance. Results for the corrosive effects of coolants on various metals at elevated temperatures are reported. The corrosion depends on the amount of ethylene-glycol oxidation products and the nature of the corrosion inhibitors.