I. FUNCTIONS OF LUBRICATING OIL

Lubricating oil in engines and machinery serves multiple critical functions beyond mere lubrication, ensuring optimal performance, extended service life, and operational reliability.

1. Lubrication

• Purpose: Forms a protective oil film between moving metal surfaces to reduce friction and wear.
• Mechanism: Creates a hydrodynamic film or boundary film to prevent direct metal-to-metal contact.
• Benefit: Minimizes mechanical wear and prolongs component life.

2. Cooling

• Purpose: Removes heat generated by friction and fuel combustion.
• Mechanism: Oil absorbs and transfers heat away from high-temperature zones to the oil cooler or less heated areas.
• Benefit: Maintains safe operating temperatures.

3. Cleaning (Detergency/Dispersancy)

• Purpose: Keeps surfaces clean, preventing deposit and sludge formation.
• Mechanism: Detergent and dispersant additives dissolve and suspend contaminants in the oil.
• Benefit: Prevents blockage, improves filtration efficiency, and sustains performance.

4. Rust and Corrosion Protection

• Purpose: Protects metal parts from oxidation and chemical corrosion caused by moisture, acids, and combustion by-products.
• Mechanism: Forms a protective layer and neutralizes acids.
• Benefit: Extends service life of metallic components.

5. Vibration and Noise Reduction

• Application: Especially important in gear systems and transmissions.
• Mechanism: Oil film absorbs shock and dampens mechanical impact.

6. Sealing

• Purpose: Prevents combustion gases from leaking past piston rings into the crankcase.
• Mechanism: Oil fills microscopic gaps between surfaces.
• Benefit: Maintains compression and improves engine efficiency.

II. COMPONENTS OF LUBRICATING OIL

Lubricating oil formulation consists of base oil and a carefully balanced additive package, blended to meet specific technical requirements.

1. Base Oil – 70% to 99% by weight

• API 1509 Classification:
  • Group I: Solvent-refined mineral oil, <90% saturates, >0.03% sulfur.
  • Group II: Hydroprocessed mineral oil, ≥90% saturates, ≤0.03% sulfur.
  • Group III: Highly hydrocracked/isomerized mineral oil, VI > 120.
  • Group IV: Polyalphaolefin (PAO) synthetic oils.
  • Group V: All other base oils (esters, silicones, PAGs, etc.).
• Key properties: Viscosity, Viscosity Index (VI), flash point, volatility, oxidation stability.

2. Additives – 1% to 30% by weight

Main additive types and functions:

• Antioxidants: Prevent oil degradation at high temperature.
• Detergents: Remove deposits from hot metal surfaces.
• Dispersants: Keep contaminants suspended and prevent sludge formation.
• Anti-wear Agents: e.g., ZDDP to protect metal surfaces when oil film is thin.
• Extreme Pressure (EP) Additives: Protect gears and bearings under heavy loads.
• Rust/Corrosion Inhibitors: Shield metal surfaces from moisture and chemicals.
• Viscosity Index Improvers: Maintain stable viscosity across temperature range.
• Pour Point Depressants: Enhance low-temperature pumpability.
• Anti-foam Agents: Prevent air entrainment that reduces lubrication efficiency.

III. LUBRICANT PERFORMANCE CLASSIFICATIONS

• API (American Petroleum Institute): Engine oil service categories for gasoline (SP, SN…) and diesel (CK-4, CJ-4…).
• ACEA (European Automobile Manufacturers’ Association): European classification for light-duty and heavy-duty engines.
• SAE (Society of Automotive Engineers): Viscosity grades (SAE 0W-20, 5W-30, 15W-40…).
• OEM Specifications: Manufacturer-specific requirements (MB, VW, BMW, Volvo, etc.).

IV. CONCLUSION

Lubricating oil is the “lifeblood” of engines and machinery, ensuring:

• Reduced friction and wear
• Efficient cooling and cleaning
• Corrosion protection
• Sustained performance and extended service life

Choosing the right oil based on engine technology, operating conditions, and international standards is critical for long-term reliability.