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. In contrast, Castrol Marine introduced Cyltech 80AW earlier this year, an 80BN oil addressing lubricant performance issues identified under slow steaming conditions when using HFO towards the top end of the permissible range.
In a letter to customers on lubricant performance across its engine portfolio, MAN says of 50-60BN oils: “oil wear varies significantly between engine types and between operational conditions”. Although mid-range lubricants were sometimes reliable “the test results from the mid-range cylinder oils can therefore not be transferred to general guidelines”.
“We welcome these recommendations from MAN,” says Paul Harrold, Castrol Technology Manager, Marine & Energy Lubricants. “They support the exhaustive bench tests and shipboard trials that led to our own recommendations on cylinder oil selection in the slow steaming era. The recommendations we make to customers must always be based on sound science.”