Gear oil is a lubricant that protects and prolongs the lifespan of the car transmission system and reduces fuel consumption. When buying gear oil, follow the instructions in your car manual. Car manufacturers generally list recommended SAE and API oil specifications and company standards, plus the amount of oil the car needs.
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Key parameters when selecting gear oils
Viscosity
Viscosity indicates the temperature range at which the oil maintains its lubricating characteristics. The viscosity grade of a lube oil is determined by SAE standards; their viscosity grades are divided into W ("Winter") oils and summer oils. The grade indicates how thick or thin the particular oil is and tells you whether it is suitable for use in summer, winter, or all year round. Low-temperature viscosity oils are marked with the letter W (for example, 75W), while high-temperature viscosity oils have no extra letters in their designation. Then there are also oils that can be used in both winter and summer. These are marked by two grades (e.g. 80W-90).
Performance characteristics
Selecting the right performance level increases protection for all gear components against wear.
- GL-1 - gear oils without additives for manual transmissions and operating under mild conditions.
- GL-2 - gear oils without additives for manual transmissions and operating under moderate conditions.
- GL-3 - gear oils with a small amount of additives for manual transmissions and operating under moderate conditions.
- GL-4 - high-additive oils for gears operating under moderate to severe conditions or axles with hypoid gears operating under moderate speeds and loads.
- GL-5 - high-additive oils for gears and axles with hypoid gears operating under highly variable conditions. Not suitable for manual gearboxes.
- GL-6 - oils for hypoid gears operating under extreme conditions. Rarely used. Not suitable for manual gearboxes.
Automatic transmissions have highly specific requirements, so performance characteristics of transmission fluids are generally determined by vehicle manufacturers.
Mineral or synthetic
Mineral oils are made from petroleum products; synthetic oils are made from artificially produced chemical compounds. There are two basic types of synthetic gear oils:
- Polyalphaolefins (PAO) - artificial polymeric mineral oils, can be mixed with other mineral oils.
- Polyalkylene glycols (PAG) - cannot be mixed with mineral or PAO oils. Not particularly common in personal vehicles.
Gear oil change intervals are there for a reason
Make sure to follow the car/oil manufacturer’s instructions and change the gear oil as often as they recommend. If you do not have the car manual, contact the car manufacturer or an authorised distributor.
