LUBRICATION METHODS

摘要

A method of lubricating a two-stroke, diesel crosshead engine comprises lubricating the engine with a cylinder oil and with a system oil, which oils are different from each other, in which the system oil is an SAE 20 or SAE 30 oil, has a total base number of at least 10 mg KOH/g and comprises :- (a) a base oil; (b) at least one detergent additive in a total amount of detergent corresponding in performance, as measured by the Hot Filtration Test, to at least 1.5 % by weight of the system oil, of a calcium alkyl salicylate detergent soap in which the alkyl group is a C<SUB>12</SUB>to C<SUB>30</SUB> alkyl group; and (c) at least one anti-wear additive. The method further comprising replenishing the system oil in the engine with a top-up system oil, in which the top-up system oil has the same additives as in the system oil previously charged to the engine but has a viscosity which is lower than that of the system oil previously charged to the engine. The system oil may be prepared by mixing a low detergency system oil with a lubricant concentrate composition which comprises a base oil and at least one detergent additive.