MAN Diesel & Turbo supports Castrol’s advice that misapplication of mid-range base number (BN) cylinder oils can cause corrosion. Castrol inform that the engine manufacturer recently issued service letters that recommend “cylinder lube oil with 70BN or higher” for latest generation super long stroke engines using higher sulphur fuel (above 1.5%-2%). MAN says it “cannot recommend” cylinder oils “with a BN level between 50 and 60” for these engines. Ship-owners have been persuaded to try a host of new mid-range lubricants on the basis that they offer a solution across the range of sulphur content in fuel oil, including during slow steaming operations.