Joe Star, Strategic Account Manager of marine fuels testing company VPS on Monday (27 October) examined the operational and financial impacts of lubrication strategies within the global merchant marine fleet, where two-stroke diesel engines are critical to world trade. The article also highlighted the essential functions of cylinder oil: protecting engine components, neutralizing corrosive by-products and minimizing deposit formation.
The article also emphasised the risks of over-lubrication, comparing current practices versus recommendations for optimizing cylinder oil feed-rates:
The Role of Cylinder Oil
More than 90% of global freight is transported by over 33,000 merchant marine vessels powered by two-stroke crosshead engines as their main source of propulsion; the two-stroke diesel engine has been the backbone of global trade and globalisation for well over half a century. Among one of the key factors supporting the reliability and uptime of these engines, keeping trade moving, is the effective performance of cylinder oil. Often referred to as the lifeblood of the engine, these oils provide critical protection to avoid abrasive, adhesive or corrosive wear from occurring within the engine; whilst maintaining a clean environment free of deposits.
Key Responsibilities of a Cylinder Oil:
- Provide a full and stable oil film throughout the cylinder liner surface to minimise adhesive wear and metal-to-metal contact.
- Provide corrosion resistance within the cylinder, through neutralising the sulphuric acid formation which occurs within the combustion chamber.
- Minimise deposit formation on piston rings and liner surfaces, by providing detergency to remove particulates and preventing the build-up of hard deposits in key component areas.
Prior to the introduction of Emission Control Areas (ECA’s) and more advanced engine designs coming to market, (designed to cater for increased pressures and temperatures, maximising thermal efficiency), the cylinder oil landscape was largely static, and performance priorities were clear. SAE 50 oil viscosity, provided the optimum film and hydrodynamic lubrication properties, whilst Base Number (BN) 70 provided sufficient neutralisation and detergency properties.
Over the last 20 years, the rapid development and introduction of differing cylinder oils has led to increased complexity onboard. The 2020 Sulphur Cap reset much of this complexity, with the industry and Original Equipment Manufacturers (OEM’s) standards coalescing on 40BN as the optimum for non-scrubbed vessels and a wide range of fuels, with some oil formulations including neutral detergency to boost clean performance.
More does not mean greater reliability
With vessel operations being far reaching and extensive, consistent reliability is paramount, from both a time and resource perspective and in ensuring an asset is maximising its earnings potential. A stable and proactive reliability strategy allows for additional initiatives to be progressed, in place of one which is reactive to reliability-based events. Due to this, there may be the viewpoint to increase the amount of cylinder oil used to further promote reliability and avoid any unforeseen lubrication issues that can be costly. As reported by the Swedish Club, the most frequent causes of main engine damage are lubrication related issues.
However, additional cylinder oil within the system, not only represents a hidden cost to enhance reliability, but can also lead to significant reliability related issues which occur and manifest over time. Additional lubricant additives that are designed to react with Sulphuric Acid within the engine, can form hard deposits on piston rings, and in extreme cases polish the cylinder liner surface. This leads to scuffing, or engine seizing, due to future lubricant injections being unable to maintain the film thickness and distribution required within the engine. The key indicator of potential over-lubrication in this instance, is the lack of depletion of Base Number when compared to the fresh Base Number of the cylinder oil in use. Note, OEM’s recommend a safe level to be in excess of 10-15mg/KOH for the majority of cylinder oil and fuel combinations in use, with both Everllence and WinGD recognising the dangers that over-lubrication can bring.
Note: The full article by Joe Star can be viewed here.
Photo credit: VPS
Published: 28 October, 2025
