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Today’s modern engines are exposing engine coolants to more severe operating conditions involving higher coolant temperatures, greater heat rejection requirements, greater metal to coolant heat fluxes, higher coolant flow rates, higher cooling system pressures, and slower deaeration. These conditions will have a tendency to accelerate oxidation/thermal degradation, reduce corrosion protection, and shorten coolant life. In efforts to simulate the increased severity in operating conditions, an accelerated oxidation and corrosion test, using a rotary pressure vessel oxidation test, was developed and evaluated to assess the oxidation/thermal stability and corrosion protection of conventional, hybrid, and extended life coolants. The test involves exposing the coolant to a high temperature oxygen rich environment under pressure with six different metal corrosion coupons. The test allows a quantitative assessment of corrosion protection of the coupons and the effects on coolant chemistry. Test results are provided on conventional, hybrid, and extended life coolants. The test has also been found to be a promising predictive tool to screen satisfactory versus unsatisfactory coolant formulations, including recycled coolants.

Significant advances have been made in heavy duty diesel engine technology to meet increasingly stringent environmental regulations for emissions. Today's heavy duty diesel engines are being designed with lighter and softer metals, greater turbocharging, increased combustion controls, and new emission reduction equipment. The cooling systems contained in these vehicles are similarly being impacted by smaller designs, new cooling system configurations, and increased usage of lighter, softer metals. Vehicle thermal loads have significantly increased due to increased power densities, higher engine temperatures, and greater metal-coolant fluxes which places greater emphasis on oxidation/thermal stability, and high temperature corrosion protection performance of the coolant. Other operating conditions (coolant flow rates, turbulence, pressure drops, deaeration) are also becoming more severe calling for improved erosion-corrosion protection, cavitation protection, and elastomer, seal, hose compatibility. This paper reviews the changes in heavy duty diesel engine technology and provides information on coolant performance in 2002-4 emission compliant engines. Predictions are also made on future engine technology and next generation engine coolants.

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