PT ANUGERAH LUBRINDO RAYA

Why Two Engines Using SAE 40 Can Require Completely Different Lubricants

Why can't one SAE 40 lubricant be used for every marine engine?

The answer lies in the engine's lubrication system.

A 2-stroke crosshead engine separates the combustion chamber from the crankcase using a stuffing box. Because of this design, the system oil circulating through the crankcase can never reach the cylinder liner.

To lubricate the liner and piston rings, a dedicated cylinder oil is injected directly into the combustion chamber.

This cylinder oil performs two critical functions:

• Forming a protective lubricating film to minimize adhesive wear between the piston rings and cylinder liner.
• Neutralizing sulfuric acid generated during fuel combustion, preventing cold corrosion through an appropriate Base Number (BN).

Depending on the fuel sulfur content and OEM recommendation, cylinder oils commonly use BN 40 or BN 70 to provide sufficient alkalinity for acid neutralization.

Meanwhile, system oil lubricates crankshaft bearings, crosshead bearings, guides, and other moving components within the crankcase. Since it remains in continuous circulation, its formulation prioritizes oxidation stability, water separation, wear protection, and cleanliness.

A 4-stroke trunk piston engine operates differently.

Because the crankcase and piston share the same lubrication system, a single engine oil must perform multiple functions simultaneously. It lubricates bearings, cools internal components, cleans combustion deposits, suspends soot, protects against wear, and prevents sludge formation.

This explains why 4-stroke engine oils typically use BN values ranging from 12 to 40, depending on fuel sulfur level, engine design, and OEM requirements.

Although both lubricants may carry the label SAE 40, their chemical formulations are engineered for completely different operating conditions.

Selecting the appropriate lubricant is therefore not simply a maintenance decision it is a reliability strategy. The correct lubricant can extend Oil Drain Intervals (ODI), reduce component wear, improve engine cleanliness, and lower the Total Cost of Ownership (TCO).

At Castrol, every lubricant recommendation is based on engine design, operating conditions, and technical performance not viscosity alone.

Because the right lubricant does more than reduce friction.

It protects productivity, maximizes reliability, and creates measurable value throughout the life of the asset.