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The strengths and weaknesses of engine coolants based on organic acid inhibitors are investigated. Recently, this technology has been approved for use by major OEM's. The coolants are expected to have a service life of at least 5 years/160,000 km as compared to the recommended 2 years/48,000 km for conventional silicate inhibited coolants. Laboratory performance tests of commercially available ethylene glycol based coolants and experimental propylene glycol based coolants are presented. These include physical properties measurement, ASTM corrosion tests, compatibility of OA and silicate coolants, tests to stress coolant performance, and electrochemical tests.

A performance review is presented for ethylene glycol and propylene glycol coolants in a heavy duty fleet test. Vehicle maintenance and testing specifications are highlighted. Aspects of regular filter change intervals and glycol segregation are underlined. The effect of glycol type on system hardware is examined. Comparisons are made by examining radiators, thermostats, water pumps, and wet-sleeve liners. In addition, inhibitor concentrations and glycol degradation products are monitored using LC, GC, and elemental techniques. Improved water pump seal life has been demonstrated using propylene glycol coolant. Comparable performance is shown for the other components.

Presented is a literature and patent review of organic acids as corrosion inhibitors for use in engine coolants. The technology is directed towards use of acid combinations or acids with conventional inhibitors because no individual acid can provide protection to the range of metals used in cooling systems. Some examples are: aliphatic monoacids with diacids, azelaic acid with aromatic acids, molybdate with two or more aliphatic acids, and sebacic acid with benzotriazole. Claimed advantages are non-depletion (‘long-life’ coolants), non-silicate (gelation and pump seal wear concerns) and non-nitrite (nitrosamine formation), and compatibility with ethylene glycol and propylene glycol.