The Valvoline blog has previously covered marine coolant technologies and how to select the right marine oil. But before you can identify the ideal lubricant formula for your vessel, understanding the different types of marine lubrication systems is essential.
To help you navigate this topic, we have put together this definitive guide covering how marine lubrication systems function.
Marine engine lubrication falls into four primary categories:
Engine oil generates a thick film that separates the moving components within the engine. Two metal surfaces in motion relative to one another produce this film, which means the pressure in this lubrication type is self-generated.
Tilting-pad thrust bearings, bottom-end bearings, and journal bearings in the main engine are all examples of components that rely on hydrodynamic lubrication.
As the name itself implies, hydrostatic lubrication differs in that the movement of parts actually prevents the oil film from forming on its own. As a result, oil pressure must be supplied externally through the use of an external oil pump. This lubrication method depends on both the inlet pressure of the oil and the clearance between the metal surfaces.
Crosshead bearings operate under hydrostatic lubrication and rely on a crosshead lubrication pump to boost the pressure.
This type occurs when forming a complete fluid film is not feasible. A thin film develops between two sliding surfaces, and the high friction between them results in a degree of metal-to-metal contact.
Boundary lubrication can arise when a shaft transitions from rest, when operating speed is very low, when load becomes excessively high, or when oil viscosity is insufficient.
Elastohydrodynamic lubrication (EHD) is the principle under which significant elastic deformation of surfaces takes place, altering both the shape and thickness of the lubricant film at the point of contact. It typically results from contact between rolling and sliding surfaces.
In marine vessels, the main engine incorporates three distinct lubricating oil systems: the main lubricating oil system, the cylinder oil system, and the turbocharger lubricating oil system.
The crankcase lubrication system operates with two pumps. One pump runs actively while the other remains on standby, ready to engage if oil pressure drops or if the primary pump fails.
Lubricating oil travels through a telescopic pipe to reach the crosshead, from which it services several components of the main engine.
First, it provides lubrication and cooling to the piston.
It then flows down to the crosshead bearing.
From there, it continues through the hydraulic power supply unit, lubricating thrust bearings, moment compensators, and torsional vibration dampers.
A turbocharger is a high-speed rotating component found in engines that harness exhaust gases to spin the turbine. Its primary function is delivering fresh air to the combustion chamber and enhancing the overall performance of the marine engine.
Because the turbocharger operates at exceptionally high speeds, its bearings are mounted on a shaft that rotates rapidly while handling substantial loads with ease.
Bearings are classified as either outboard or inboard based on their position along the TC shaft.
Outboard bearings are positioned on the exterior side of the rotating turbine and compressor blade on the shaft.
Ball and roller bearings are the most widely used option in this position. Newer TC designs also support the use of sleeve bearings as an alternative to conventional ball and roller bearings.
A key advantage of outboard bearings is their accessibility, which simplifies maintenance and servicing. They are also more straightforward to remove and replace compared to other bearing types, and they do not require removal of the compressor wheel — saving both time and effort.
However, they are susceptible to overloading and can deteriorate quickly when subjected to such conditions.
For this reason, their lubrication system demands careful upkeep. Lubrication can be supplied either through an external M/E LO system fitted with a fine filter or through a self-contained system comprising a pump, filter, cooler, TC system oil, alarm, and related components.
The lubrication system for outboard bearings is made up of:
These bearings are situated inside the rotating turbine and compressor blade on the TC shaft.
Sleeve white metal bearings are the standard choice for inboard positions.
Unlike outboard bearings, inboard bearing systems lack a dedicated sump; instead, lubricant is drawn from the main lube oil system via the gravity tank.
Inboard bearings offer a range of notable advantages.
To begin with, they occupy less space than outboard bearings.
They also provide superior cooling performance, allowing them to function more effectively at elevated temperatures.
Relative to outboard bearings, inboard bearings have longer overhaul intervals, which translates to an extended service life.
Their primary drawback is limited accessibility — replacing or servicing inboard bearings requires prior removal of the rotor. Additionally, the risk of oil contamination is elevated because the system draws lubricant from the main lube oil supply.
Cylinder lubrication is handled by a dedicated cylinder lubrication system, which is responsible for lubricating the piston rings.
The cylinder lubrication system serves multiple functions, including:
As a general guideline, the alkalinity of the cylinder lubricant should correspond to the sulfur content of the heavy fuel oil (HFO) in use. If your engine runs on low-sulfur fuel, consult the cylinder oil manufacturer to identify the most appropriate product.
Several cylinder lubrication systems exist and can be grouped into two categories: traditional and modern.
Traditional cylinder lubrication systems include:
Modern cylinder lubrication systems include:
Despite their considerable capabilities, marine engine components remain vulnerable to friction, corrosion, and wear and tear — in fact, these are among the most persistent challenges they face.
Keeping the engine properly lubricated is critical to ensuring it operates efficiently.
The lubricating system may either be integrated into the main engine lubricating system or function as a standalone unit.
To fully protect the turbocharger bearing lubrication system, an effective marine engine lubrication oil should possess the following properties:
Viscosity refers to the thickness of oil and its capacity to flow under varying temperatures. A high-viscosity oil is thicker and forms a robust film around engine components, offering better protection at elevated temperatures. Low-viscosity oils, by contrast, are thinner and flow with greater ease.
Like passenger car engine oils, marine engine oils are available in either mono-grade or multi-grade formulations.
Opting for a multi-viscosity marine engine oil is generally the superior choice. Valvoline Premium Blue Extreme 5W-40 is one such product. Multi-viscosity oils cover a broader temperature range, making them suitable for year-round use across diverse operating conditions.
Combustion of fuel releases fumes containing sulphuric acid, which can lead to acidic corrosion. Alkalinity is therefore a critical consideration when selecting a marine engine oil, as it governs the oil's ability to neutralize acidic attack.
Marine engine lubricants are exposed to air, making the presence of oxygen unavoidable. At high temperatures, oxidation accelerates, leading to sludge buildup, bearing corrosion, and acid formation. Anti-oxidation and anti-corrosion additives are incorporated into the lube oil to counteract these effects.
Load-carrying capacity is directly tied to oil viscosity. Given the substantial weight of internal marine engine components, the lubricant must possess sufficient load-carrying capacity to handle the pressures within the engine. Inadequate capacity can lead to metal-to-metal friction and accelerated engine degradation.
Flash point represents the minimum temperature at which a lubricant vaporizes. It should consistently remain above 220°C — the higher the flash point, the lower the fire hazard risk as oil temperature rises.
Detergency is delivered through the inclusion of metallic-based additives with enhanced cleaning capabilities. These additives prevent small deposits from accumulating on metal surfaces. In two-stroke engines, they remove contaminants from the ring pack area and maintain a clean combustion space.
The continuous movement of engine components generates significant heat. To guard against overheating, the oil must transfer this heat away from internal parts, making good thermal stability and conductivity essential properties.
Valvoline's marine engine oils are engineered to satisfy all of the characteristics described above.
Our Premium Blue™ is one prime example — a top-tier engine oil designed for diesel engines and heavy-duty applications. It is crafted from high-quality base oils and specialized additives that neutralize harmful acids, reduce engine wear, and help prevent breakdowns. It also delivers reliable engine protection in the most extreme weather conditions, and its distinctive antioxidant additive package maximizes engine cleanliness while minimizing oxidation risk.
For more than 150 years, Valvoline has continuously advanced its technologies to supply boat owners with the finest engine oils available. Every marine lubricant in our lineup undergoes rigorous testing to ensure maximum engine performance, minimal downtime, and improved fuel efficiency.
Beyond premium engine oils, Valvoline also provides a comprehensive range of lubricant solutions, including:
Browse our complete marine lubricant lineup on our website. For further product details, refer to our technical data sheets or get in touch with your nearest Valvoline distributor!
