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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.