These high-performance lubricants are formulated specifically to endure the intense demands of transmission and differential assemblies

Where engine oils focus on combustion byproducts, gear oils are built for shear resistance and load-bearing durability

Different gear oil formulations address distinct operational scenarios—from light-duty transmissions to extreme-duty industrial gearboxes

Knowing how they vary allows you to select the optimal fluid, boosting performance and prolonging gear longevity

Gear oil viscosity is primarily categorized using standards established by the SAE

You’ll commonly encounter multi-grade options such as 75W-80, 85W-90, and single-grade 140 for heavy applications

The prefix number reflects cold-weather fluidity; the suffix denotes viscosity at normal operating heat

For example, اتوسرویس داوود a 75w-90 gear oil flows easily in cold weather but still provides adequate thickness when hot

Selecting the right viscosity is essential—insufficient thickness leads to metal-on-metal contact, while excessive viscosity increases parasitic loss and overheating

Gear oils fall into two primary categories: conventional petroleum-based and advanced synthetic blends

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

They work well in standard applications with moderate temperatures and loads

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

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

Synthetics are ideal for extreme conditions such as heavy-duty trucks, off-road vehicles, and industrial gearboxes that run continuously under high stress

Gear lubricants are rated according to standardized performance tiers

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

GL-1 is for light-duty manual transmissions with low stress

GL-3 and GL-4 are common in modern passenger vehicle manual transmissions

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

GL-6 was developed for ultra-high-performance systems but has largely been phased out due to synchronizer wear concerns

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

Specialized additives are blended to address wear, corrosion, friction, and load resistance

Extreme pressure additives prevent metal-to-metal contact under heavy load

AW additives minimize pitting, scuffing, and micro-wear on gear teeth

These agents neutralize acidic byproducts and prevent oxidation-induced degradation

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

It is important to note that not all additives are compatible

Using non-recommended fluids in limited-slip units may result in grinding, vibration, or complete clutch pack failure

Some lubricants are engineered exclusively for particular transmission types

Transmission fluids for automatic transmissions are not interchangeable with manual transmission or differential oils

Some require standard gear oil, others demand specialized low-viscosity synthetics

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

Always follow the recommendations in your owner’s manual or equipment guide

A single wrong fluid choice can cost thousands in repairs

To choose correctly, evaluate SAE viscosity, API GL rating, mineral vs. synthetic base, and additive compatibility

Taking the time to understand these differences ensures your gears run smoothly and last longer

Never guess—precision lubrication is non-negotiable in mechanical systems

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