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.Results demonstrate that the heat transfer performance of propylene glycol based engine coolants is comparable to ethylene glycol based coolants, and qualitatively substantiate improved heat transfer for PG based coolants in nucleate boiling heat transfer.