1. Thermal and Oxidation Stability: The oil must resist degradation under the high temperatures and oxidative conditions within the engine. Deterioration leads to sludge formation, increased viscosity, and reduced lubricating effectiveness. The oil needs to remain stable for extended periods under normal operating conditions.
2. Viscosity: Appropriate viscosity is essential for maintaining an adequate oil film thickness between moving engine components. This prevents metal-to-metal contact, reducing wear and preventing damage. Too high a viscosity hinders oil flow, increasing friction and temperature. Conversely, viscosity that is too low increases the risk of metal-to-metal contact. The viscosity grade must be selected based on the engine's operating temperature and load.
3. Total Base Number (TBN): TBN measures the oil's alkalinity and its ability to neutralise acidic byproducts of combustion. Acids formed during combustion are corrosive and can damage engine parts. Sufficient alkalinity is crucial to neutralise these acids, protecting against corrosion and extending the oil's service life. A minimum TBN is usually specified for the oil to ensure sufficient protection.

(i) Water is present :

• Identify and eliminate the source of water ingress.
• Run the purifier at a low feed rate.
• Drain water from the crankcase after allowing it to settle.
• Conduct batch purification: Transfer the oil to a settling tank, heat it, allow water to settle, and drain it.
• Continue purification and run the engine at reduced load.

(ii) Alkalinity has fallen :

• Reduce engine load to minimize acidic byproduct formation.
• Raise jacket cooling water temperature to prevent dew formation on liner walls, which leads to acid production.
• Can add some oil of cross head type engine if TBN of trunk piston engine crankcase oil has fallen below 8. Ensure "MAKER" is same.

(iii) Viscosity has changed appreciably :

• Investigate and rectify the cause of viscosity change, such as fuel contamination.
• Partially drain old oil and replenish it with fresh oil if available.
• Run the engine at a reduced load to limit wear.

(iv) Carbon content has increased :

• Check for improper combustion caused by fuel system issues (e.g., faulty fuel pump, injector, or incorrect fuel temperature).
• Address blow-past due to worn liners or piston rings.
• If an overhaul is not possible, partially replace old oil with fresh oil if available.
• Run the engine at reduced load and maintain continuous purification to manage carbon content.