What Makes Marine Oil Unique?

Marine oils are a specific area of lubrication due to the unique operating conditions, design, and fuel types in use. Whilst Sulphur levels in fuels are reducing as part of a global effort to reduce emissions, existing engines where designed to use specific chemistries whether low, medium, or high speed.

From 1st January IMO 2020 limits the amount of Sulphur in HFO to 0.5%. This move is designed to reduce SOx emissions reducing acid rain, loss of crops, damage to marine and aquatic life and respiratory symptoms within the global population. The reduction in Sulphur and increased use of Dual fuels has changed the requirements of typical lubricating oils with regards to Alkalinity which will be discussed further.

Lubricating oil is an essential element for operating machinery. It is responsible for both lubrication and cooling reducing metal to metal contact and therefore reducing wear of vital components. Many types and grades of oils are available, depending on the working condition, operation, and requirements of the machinery.

Total Base Number (BN)

For trunk piston or 4 stroke engines, lubricating oil is used for both the pistons and liners. Here oil comes into direct contact with products of combustion which will contain acidic Sulphurous compounds which can lead to corrosion of vital moving parts. Lubricating oils are designed to have a high base number (Alkalinity) which will neutralise any acidity preventing corrosive wear. For two-stroke engines a separate grade is used to lubricate cylinders and hence its base number will depend on the fuel grade in use i.e. HFO or LSFO.


Oxidation has always been the nemesis of lubricating oils for many years; hence, large amounts of development time is dedicated to its control. As bulk oil temperatures rise, the rate of oxidation increases doubling every 10°C above 85°C. Oxidation leads to sludging, acids and oil thickening all of which reduce the effective life of any lubricant.

Load Carrying Capacity

Large marine engines are subject to different types of lubricating regimes from simple hydrodynamic to more complex boundary lubrication. It is vital to maintain lubrication, preventing metal to metal contact, therefore reducing premature wear. Using a well formulated marine oil from a specialist company will extend the service life of your engine and marine equipment, reducing downtimes and unplanned maintenance.

Detergency / Dispersancy

As with all engines it is vital to keep engines clean, suspending contaminants so they can be removed by filters and oil clarifiers. In two stroke engines it is especially important to keep the ring pack and combustion areas as clean as possible.

Flash point

Fires need to be avoided on board ships at all costs. Passenger ships in mid Atlantic can ill afford any accidents which may lead to the loss of life especially with modern liners carrying thousands of passengers. Whilst not a general rule, most marine engine oils will not contain any lighter base oils and hence the flash point is typically above 220°C. Flash point is the lowest temperature at which oil vapours will burn without leading to a continuous fire; hence, flash point. This gives an indication of flammability both prior to filling and in use where fuel dilution must be avoided.


Ships and marine vessels are surrounded by water and hence to try and remove all possible contamination would be futile. Correctly formulated marine oils shed water rapidly allowing separators to remove water quickly and efficiently. Should marine oils emulsify they would lose lubricating properties resulting in metal to metal contact, wear, pitting and corrosion.

Exol Lubricants has supplied cargo and passenger shipping in addition to pleasure craft for many years. Exol Lubricants has a proven track record in providing technically correct products and bespoke solutions to the marine sector.