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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.

Test results have been obtained on the thermal performance of aqueous mixtures of propylene-glycol and ethylene-glycol for conditions simulating automotive engine operation. For the present study, thermal performance is defined as the test section surface temperature for a given set of operating conditions. In addition to testing over a wide range of surface heat fluxes up to 2.3 MW/m2, data were also obtained at different mixture concentrations. For all cases considered, both coolant mixtures provided similar results.

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.

Propylene Glycol has generated interest as a base material for coolant/antifreeze for internal combustion engines that would be superior to existing coolants in product safety. Previous studies have presented the merits for propylene glycol engine coolants developed for use in heavy duty engines. The automotive or light duty market has different requirements and different concerns for the performance of a cooling fluid. Also, since this segment includes the vehicles owned and maintained by the general public, the safer nature of propylene glycol products resulting from their lower relative toxicity has increased importance. Products have been developed for this market using inhibitor chemistry similar to that used historically for engine coolants. The results of testing of these products against standards of performance for engine coolants for light duty engines are discussed.