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An inhibitor package which is silicate-, nitrate-, borate- and phosphate-free has been developed as the basis for a world-wide automotive coolant formulation. The formulation contains aliphatic mono- and dicarboxylic acids and tolyltriazole as the sole inhibitors. Formulations containing carboxylic acid inhibitors have been studied in ASTM bench tests and found to sufficiently protect all prevalent cooling system metals. In addition, fleet tests have shown that carboxylic acid inhibitors deplete much more slowly than conventional inhibitors, making possible a much longer life coolant. Results from laboratory tests which simulate extended usage indicated that carboxylic acid-containing coolants have a significantly longer life span for the protection of all cooling system metals. Finally, the carboxylic acid/tolyltriazole inhibitor package is completely adaptable to a propylene glycol base.

The effect of small amounts of silicate on coolant performance has been studied. The corrosion protection provided by different coolant technologies was evaluated for different silicate contents. This work includes results from electrochemical tests and static and dynamic heat-rejecting tests on aluminum surfaces. The results indicate that small amounts of silicate have a negative effect on the corrosion protection of aluminum. Depletion of silicates can therefor be expected to affect aluminum heat-rejecting surfaces. The use of carboxylic acid corrosion inhibitors can overcome this problem.