Overview
Special trunk oil is a lubricant for medium-speed four-stroke trunk-piston engines running on low-sulphur distillate fuels. Grades: 30, 40. Its published base number is 12 mg KOH/g. For high-sulphur residual fuel, see Trunk oil or super trunk oil.
In marine and stationary diesel service, the base number is matched to the sulphur content of the fuel: higher-sulphur fuels need a higher base number to neutralise the acids formed in combustion. The specification table lists each grade with its test methods.
