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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.

This paper describes the properties of an engine coolant that uses a potassium propionate solution as base fluid. Although alternatives for ethylene glycol are known, e.g. propylene glycol and glycerin, the use of a salt based coolant for high temperature applications has seldom been considered as a viable option due to the intrinsic corrosiveness of such salt solutions. The salt based coolant offers freezing as well as boiling protection and has thermal properties that allow for usage in standard combustion engines. Volumetric heat capacity and viscosity are very similar to glycol based analogues, while its thermal conductive is substantially higher. Thermal experiments indicate that the potassium propionate coolant is highly effective in suppressing localized boiling phenomena. Due to its chemical nature the coolant has superior oxidation stability. The coolant has the further advantage of being readily biodegradable and has a low toxicity.

The use of glycol based coolants in combination with EPDM hose materials has been used in the internal combustion engine for over 25 years. EPDM remains the most widely used elastomers due to its advantageous price to performance ratio in this field of application. The major car manufacturers are calling for better fuel consumption by means of weight reduction and improved aerodynamics of the car. These two factors lead to a steady and continuous increase of the under-bonnet temperatures. Consequently the operating temperatures of the cooling circuits have increased. New metal alloys are used for the production of engines in order to reduce weight. These new metal alloys coupled with the higher temperatures dictate appropriate changes in the composition of cooling liquids. Particular attention has to be paid to the stabilisation packages and modification of the materials used in the EPDM hose. These changes lead to an influence of the long-term performance of EPDM hose materials.