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Modern engine coolants have advanced significantly in the last decades. This advancement focused mostly on the selection of more performing and robust additive technologies. Nevertheless, the majority of coolants still in use today use the same base fluid as 60 years ago, namely a mixture of water and monoethylene glycol (MEG). MEG is a vicinal alcohol and thus relatively susceptible to oxidation. The oxidation of MEG results in the formation of short chain acids such as formic and glycolic acid, which lower the pH of the coolant, increase corrosiveness and reduce additive stability. Increased power output in the modern engine, sometimes combined with accidental or design related air intake may result in such severe MEG oxidation that optimal coolant performance becomes jeopardized. This paper presents data on the oxidation stability of a fully formulated carboxylate salt based engine coolant. The base fluid is comprised out of an aqueous solution of potassium propionate. Corrosion inhibition is provided by the addition of an optimized additive package. The data is compared with that generated on two long-life monoethylene glycol based engine coolants. The new coolant looks virtually indifferent to oxidation, despite the extreme testing circumstances. No significant acidification occurred resulting in a highly stable pH and little or no discoloration of the liquid. Additive concentrations were hardly affected. The corrosion protection effectiveness remained excellent, resulting in very low soluble iron concentrations and no deposit formation.
coolant, oxidation stability, monoethylene glycol, potassium propionate, carboxylate
De Kimpe, J.
Chevron Technology Ghent, Global Coolants Technology, Ghent,