METHOD FOR REDUCING PISTON DEPOSITS IN A MARINE DIESEL ENGINE

A method of reducing the incidence of deposits on the pistons of a 4-stroke marine diesel engine during operation of the engine when it is fuelled with a marine residual fuel meeting the ISO 8217 2017 fuel standard for marine residual fuels and having a sulphur content of more than 0.1% and less than 0.5% by mass. The method comprises lubricating the engine using a lubricating oil composition comprising: (a) at least 50% by mass, based on the mass of the composition, of an oil of lubricating viscosity; (b) 5 to 25% by mass, based on the mass of the composition, of an oil-soluble or oil-dispersible alkali metal or alkaline earth metal salicylate detergent, or a mixture of two or more oil-soluble or oil-dispersible alkali metal or alkaline earth metal salicylate detergents; (c) 0.1 to 10 % by mass, based on the mass of the composition of one or more oil-soluble or oil-dispersible ashless dispersants; and optionally, (d) 0.1 to 10 % by mass, based on the mass of the composition of a polyalkylene-substituted succinic anhydride.