Marine Oil Types by Engine

Which marine lubricant an engine needs is decided first by its type. Slow-speed two-stroke crosshead engines — the main propulsion of most large merchant ships — use two separate oils: a once-through cylinder oil injected onto the liner and lost to combustion, and a recirculating system oil that lubricates the crankcase, crosshead, bearings and drives, and is cleaned and reused. Medium- and high-speed four-stroke trunk-piston engines — common as auxiliaries, gensets and the main engines of smaller vessels — use a single trunk-piston engine oil that lubricates the cylinders and the crankcase together, so it must handle combustion by-products and crankcase duty at once. Auxiliary systems add their own oils: hydraulic oil for steering gear and deck machinery, gear oil for reduction gears, and turbine and compressor oils. Getting the class right is the first decision; only then do base number, viscosity grade and OEM approval narrow it to a specific product.