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A high horsepower, low heat rejection diesel engine is being developed to meet future Army heavy combat vehicle requirements. This engine features high power output in a compact design that is oil-cooled allowing for a significant reduction in radiator size. This design requires a lubricant which can survive a sump temperature of 160°C, for 300 hours with transient sump temperature surges to over 177°C. A comprehensive high temperature lubricant development program has been initiated to address the need for this new design. A modified Cummins 10 liter diesel engine was used to simulate the operating condition of this low heat rejection engine. The premium commercial lubricant that was tested survived only 58 hours before completely losing oxidative stability. Several of the experimental lubricants completed the 200-hour peak torque endurance test.

An engine rig test and a scuffing BOCLE test have been used to investigate the lubricity of low sulfur diesel fuels and its relationship with unit injector wear in heavy duty diesel engines. The rig test effectively ranks 11 selected fuels/fluids according to their actual performance. The scuffing BOCLE test correlates with the rig test by showing the same ranking capability, and it is easy to perform. A similar correlation has been established using ISO reference fuels. The scuffing BOCLE test has been used to study 37 fuels randomly sampled from the field. The data shows that there is indeed a reduction in lubricity of low sulfur fuels. The variation in lubricity of low sulfur fuels is also much greater than high sulfur fuels. Data in this study shows that transition from good to poor lubricity usually occurs between 2500 to 3000 grams in the scuffing BOCLE.