A Study of Coolant Oxidation Phenomena in High-Power-Efficiency Engines by Exploring Different Lab Test Methodologies

In conjunction with modern engine design and long term reliability needs, the resistance of engine coolants to oxidative stress has become an increasingly important feature. This paper describes the results of a study that evaluated the influence of parameters such as temperature, aeration and catalytic metal interaction on the oxidation stability of engine coolants. Three different test set-ups were used in which the selected conditions put variable weights to the contribution of each parameter. A comparison was made of the oxidation resistance of multiple high quality OEM approved coolant products with different additive technologies. This work is different from previous investigations focusing mainly on the behavior of coolants in single test conditions. The glycol oxidation level was evaluated by measuring the pH together with the determination of glycolate, formate and oxalate content of the samples by means of anion exchange chromatography and the repeatability of the test conditions was examined. The amount of ethylene glycol oxidation products found in these new test methods correlates with the amount of oxidation products that have been observed in the field. The results reveal that oxidative resistance is highly dependent on the test conditions, both quantitative when comparing the amount of oxidation products, as well as qualitatively when comparing different coolants. The data illustrates that a good understanding of the mechanisms that cause glycol oxidation in cooling systems is crucial for the selection of relevant laboratory test conditions.