Gear oils are specialized lubricants designed to protect and enhance the performance of gear systems in vehicles, machinery, and industrial equipment

Unlike engine oils, gear oils must handle high pressure, extreme temperatures, and heavy loads without breaking down

There are several types of gear oils, each formulated for specific applications and operating conditions

Understanding the differences between them helps ensure the right choice for your equipment, improving efficiency and extending component life

The SAE viscosity grading system is the industry standard for identifying gear oil flow characteristics

Common SAE grades include 75W-90, 80W-140, 85W-140, and straight-weight options like SAE 90 and SAE 140

The "W" number measures viscosity in freezing conditions, while the trailing number shows resistance to flow when hot

This dual-grade formulation ensures smooth engagement in freezing temps and robust film integrity during heavy use

An improperly matched viscosity can result in accelerated wear, reduced fuel economy, or dangerous thermal runaway

Another key distinction is between mineral-based gear oils and synthetic gear oils

Derived from refined petroleum, these oils offer cost-effective performance for standard applications

They perform reliably in everyday driving conditions and light industrial settings

Synthetic variants are laboratory-created to maximize thermal and mechanical resilience

Synthetics maintain viscosity integrity over extended periods and withstand prolonged high-stress operation

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Gear lubricants are rated according to standardized performance tiers

API service categories—GL-1 to GL-6—indicate the level of extreme pressure protection

Designed for minimal pressure environments, GL-1 oils are used in simple, non-synchronized transmissions

GL-3 and GL-4 are for moderate to high-speed applications like passenger car transmissions

GL-5 is the most common for heavy-duty axles and differentials that require extreme pressure protection

GL-6 is used in high-performance applications but is less common today due to compatibility issues with synchronizers in modern transmissions

Never assume—always verify the manufacturer’s specified API grade for your gear system

Many formulations include performance-enhancing additives tailored to unique operational needs

EP additives form protective films that withstand crushing forces and prevent scoring

Anti-wear agents reduce friction and surface damage

Corrosion inhibitors protect against moisture and rust

Some formulations also include friction modifiers to improve shift quality in manual transmissions

Mixing incompatible additives can lead to chemical reactions or performance failure

For example, some limited-slip differentials require special friction modifiers and using the wrong oil can cause clutch slippage or chatter

Not all gear oils are interchangeable across vehicle systems

ATF contains friction modifiers and detergents unsuitable for manual gearboxes and differentials

Even within manual transmissions there are variations

Vintage models often call for conventional 80W-90, while modern units specify API GL-4 or GL-5 synthetics

Deviation from OEM guidelines risks warranty voidance and mechanical damage

A single wrong fluid choice can cost thousands in repairs

The optimal gear oil balances temperature performance, load protection, and اتوسرویس داوود system compatibility

Proper selection minimizes downtime, reduces maintenance costs, and maximizes equipment lifespan

When in doubt, consult a professional or refer to the manufacturer’s guidelines

Correct gear oil selection is fundamental to safe operation, regulatory compliance, and long-term asset value