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Engine dynamometer testing was done to demonstrate the effectiveness of propylene glycol based engine coolants in removing heat from a modern gasoline engine, and to compare that heat transfer performance with similar ethylene glycol based engine coolants. Coolant concentrations ranging from 30% to 70% in both propylene and ethylene glycol were examined. The testing was done on a production 3.8 litre V6 engine, on a computer controlled dynamometer stand. The engine was instrumented to obtain temperature measurements at critical points in the engine, including the bridges between the exhaust and intake valves of four cylinders, and engine block cylinder walls near the combustion chamber. The thermocouple locations were selected at or near known hot spots in the engine. Coolant temperatures, engine speed and dynamometer load were controlled to simulate a range of operating conditions and ambient temperatures.

Propylene glycol (PG) based engine coolants have been tested in both heavy-duty and automotive service. Results of comparison tests between PG base engine coolants and traditional ethylene glycol (EG) base coolants are presented in this summary paper. The detailed testing program included laboratory testing for corrosion protection, freeze protection and heat transfer performance, engine testing for corrosion protection, low temperature performance and heat transfer, and extensive fleet testing in both automotive and heavy-duty applications. The testing has proven that PG is an excellent base fluid for modern engine coolants, providing the necessary heat transfer properties, freeze protection, boil-over protection and, when adequately inhibited, corrosion protection.

On highway and proving ground vehicle tests were conducted in the Southwestern United States to compare the performance of propylene glycol and ethylene glycol based coolants. A cross-section of vehicles encompassing pickup trucks, large and small cars, a minivan and a sport utility vehicle from various manufacturers were included in the program. Test protocols were completed with vehicles ballasted to curb weight with a four passenger load, with and without maximum recommended weight trailers. On highway driving schedules were run simultaneously with each vehicle pair. Two sets of tests were completed with each pair; once with ethylene glycol/water coolant and once with propylene glycol/water coolant. This was done in an AB/BA test sequence to reduce the impact of different ambient conditions between test. Ambient temperatures during the testing ranged from 35°C to 50°C.