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High-temperature lubricant (HTL) requirements for future U.S. Army ground vehicles were investigated. A single-cylinder diesel engine (SCE-903) was successfully modified to operate at increased cylinder liner temperatures and to serve as a tool for HTL evaluation. Oil D, one of six lubricants evaluated, completed 200 test hours at an average cylinder wall temperature of 247°C and an oil sump temperature of 166°C with only minor oil degradation. However, improved piston cleanliness is desired.

Several multiviscosity grade oils were subjected to a special 240-hour endurance test procedure in an Army high-output two-cycle diesel engine, and certain of the oils were laboratory tested in the Army's multifuel, four-cycle compression ignition engine and in the Army's air-cooled four-cycle diesel tank engine. Certain of the lubricants were also subjected to standard hydraulic/power transmission tests because acceptable power transmission performance will now be a formal requirement in the D-revision to the engine lubricant specification MIL-L-2104. Parallel to these laboratory evaluations, pilot field tests were conducted in combat/tactical vehicles (engines and power shift transmissions) at three Army bases. The limited field tests indicated that the use of arctic/conventional multiviscosity grade lubricants at ambient temperatures up to 38°C(100°F) may be possible, and their introduction under MIL-L-2104 should be pursued.