Gear Oil is a high-viscosity, high-load lubricant specifically formulated to protect gears, bearings, shafts, and synchronizers operating under extreme pressure, sliding contact, shock loads, and elevated temperatures. Unlike engine or hydraulic oils, gear oils are engineered to perform reliably in boundary and extreme-pressure lubrication regimes where metal-to-metal contact is unavoidable.
Gear oils are essential for maintaining mechanical efficiency, surface integrity, and long service life in both automotive and industrial gear systems, including transmissions, differentials, gearboxes, and heavy-duty industrial drives.
Core Functions of Gear Oil
Lubrication & Film Formation
Creates a strong, durable oil film that separates gear teeth and bearings,
preventing direct metal-to-metal contact.
Extreme Pressure (EP) Protection
EP additives chemically react with metal surfaces under high load to prevent
scuffing, seizure, and welding.
Heat Dissipation
Carries away heat generated by friction and gear meshing.
Wear & Fatigue Protection
Prevents pitting, micropitting, spalling, and surface fatigue of gear teeth.
Corrosion & Rust Prevention
Protects metal surfaces from moisture, oxidation, and chemical attack.
Noise & Vibration Reduction
Ensures smoother gear engagement, reducing noise, vibration, and harshness (NVH).
Key Performance Characteristics
High Viscosity & Film Strength
Maintains a protective lubrication film under high contact pressure and
shock loading conditions, essential for hypoid, spiral bevel, and worm gears.
Extreme Pressure Capability
Sulfur–phosphorus EP additives form sacrificial protective layers that prevent
scuffing, adhesive wear, and surface welding under heavy loads.
Thermal & Oxidation Stability
Resists oil degradation, sludge formation, and viscosity breakdown at
elevated operating temperatures, enabling longer drain intervals.
Anti-Foam & Air Release Properties
Prevents air entrainment that can reduce lubrication efficiency and cause
erratic temperature control.
Metal Compatibility
Properly formulated gear oils protect steel gears as well as bronze and brass
components. GL-4 oils are generally safer for yellow metals.
Typical Mechanical & Performance Properties
SAE Viscosity Grades: 75W-85, 75W-90, 80W-90, 85W-140
ISO VG Grades (Industrial): 150, 220, 320, 460, 680
Viscosity Index: 90 – 160+
Flash Point: 180°C – 260°C
Pour Point: –12°C to –45°C
EP Load Stage (FZG): ≥ 12
Oxidation Life: 2,000 – 10,000+ hours
Gear Oil Classification
By SAE Viscosity (Automotive – SAE J306)
75W / 80W for cold-temperature flow
90 / 140 for high-temperature protection
Multigrade oils provide year-round performance.
By API Service Classification
API GL-4 – Moderate EP protection for synchronized transmissions
API GL-5 – High EP protection for hypoid differentials and axles
API MT-1 – Heavy-duty non-synchronized truck transmissions
By Base Oil Type
Mineral Gear Oils – Cost-effective for standard duty
Semi-Synthetic Gear Oils – Improved stability and oxidation resistance
Fully Synthetic Gear Oils – Superior performance in extreme temperatures
Industrial Gear Oil Classification (ISO 12925)
CL – Rust & oxidation inhibited oils
CLP – EP gear oils
CKC – High-load EP oils
CKS – Synthetic industrial gear oils
Specialized Gear Oils
Hypoid Gear Oils – For sliding and offset gears in automotive axles
Worm Gear Oils – High lubricity, often compounded for bronze gears
Wind Turbine Gear Oils – High micropitting resistance and long drain life
Marine Gear Oils – Water resistance and corrosion protection
Gear Oil Selection Criteria
Gear type (spur, helical, bevel, hypoid, worm)
Load and torque conditions
Operating temperature range
Metal compatibility (yellow metals)
OEM and equipment specifications
Environmental exposure (moisture, dust, marine)
Maintenance & Oil Life Management
Regular oil analysis for viscosity and wear metals
Proper filtration and contamination control
Correct oil change intervals
Avoid mixing incompatible grades and formulations
Applications of Gear Oil
Automotive – Manual transmissions, axles, differentials, transfer cases
Industrial – Gearboxes, crushers, mills, conveyors, rolling mills
Construction & Mining – Excavators, loaders, haul trucks, drilling rigs
Agriculture – Tractors, harvesters, PTO systems
Marine – Propulsion systems, winches, thrusters
Renewable Energy – Wind turbine gearboxes
Benefits of High-Quality Gear Oils
Reduced gear wear and failure
Lower operating temperatures
Improved energy efficiency
Extended oil drain intervals
Reduced maintenance and downtime