The West of England P&I Club issued a Loss Prevention Bulletin on marine diesel engine lubrication.
In recent months several entered vessels have experienced main engine breakdowns caused by heavily contaminated lubricating oil. All of the vessels were relatively new.
Modern marine diesel engines are technically complex and are becoming increasingly powerful and efficient. However, newer engines can be less forgiving than older units if not operated, maintained and lubricated correctly.
Lubricating Oil
The lubrication of moving parts is crucial to diesel engine performance and longevity. Lubricating oil reduces friction between components, separates opposing surfaces and prevents metal-to-metal contact. It also acts as a coolant and mitigates the effect of corrosion. However, the condition of the oil tends to deteriorate with use, mainly due to contamination and chemical activity.
The manufacturer’s manual for the engine will provide details of the quality and properties of lubricating oil required. The manual will also include guidance on how the oil should be monitored and maintained while the engine is running to ensure that it remains suitable for use. Such advice is generally based on research findings, operational experience, ongoing analysis and other factors including technical common sense. The details will also include a margin of error to minimise the risk of the engine being damaged as the lubricating oil deteriorates, but the extent of this margin is not known to the user. Therefore it is not possible for the user to determine with any degree of confidence whether the outcome of exceeding the limits set by the engine manufacturer will be relatively harmless or potentially disastrous.
Although the engine manual contains important information about the lubricating oil and specifies key requirements and constraints, the fundamental principles rarely differ:
- The viscosity of the lubricating oil must remain within certain prescribed limits. Normally, oil viscosity increases during operation. If it decreases, this may signify an ingress of low viscosity fuel. Increased or decreased viscosity may lead to improper lubrication and thermal distortion.
- The oil must not contain excessive amounts of water or insoluble foreign particles as their effects become increasingly harmful during operation, resulting in poor lubrication and mechanical damage.
- The oil must be capable of protecting the components of the engine from corrosion caused by aggressive chemicals. The ability of the oil to neutralise acidic compounds is termed the Total Base Number (TBN) or, alternatively, the Base Number (BN). The TBN of lubricating oil generally decreases with use. Acidic corrosion may occur if the TBN falls below the threshold specified by the manufacturer of the lubricating oil, resulting in excessive wear and reducing the life of the parts.
- The flash point of the lubricating oil should remain within the range set by the manufacturer. A flash point lower than specified may signify the presence of lighter hydrocarbons, possibly indicating that the oil has been affected by diesel fuel.
While in operation, the lubricating oil normally passes through mechanical filters to extract solid foreign particles, and centrifugal separators to remove other impurities and water. It is essential that both are inspected and maintained entirely in accordance with manufacturer’s instructions.
The viscosity, flash point and TBN of lubricating oil can only be restored by a full or partial oil change.
Changing the Lubricating Oil
If the necessary make and type of lubricating oil cannot be obtained, the safest option may be to change the lubricating oil completely to avoid any incompatibility problems such as foaming or deposit formation which may result in blocked filters and lubrication starvation.
For more information you may read the Loss Prevention Bulletin below:
Source: West of England P&I Club
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