Vehicles can move as a result of a complex system of gears contained in its transmission, or gearbox. Those gears can function in concert thanks to the gear oils that flow among them. Gear oils are specially designed lubricants with properties that allow gears to turn effectively. There are several types of gear oil.
All gear oils have the same five basic properties: thermal and oxidation stability (the ability to withstand temperature changes and chemical changes), the ability of protect against rust and corrosion, sealant compatibility, the ability to remain stable at extreme pressure levels, and proper viscosity (the ability to flow with varying amounts of friction). Gear oils are either mineral oils or synthetic oils. The Society of Automotive Engineers (SAE), the International Organization for Standardization (ISO) and the American Petroleum Institute (API) are organizations that establish standards for gear oils in the United States and abroad.
Extreme pressure (EP) oils are a type of gear oil that contains additives enabling the oil to remain stable under the great pressure that builds up in high-performance gears. These additives include chlorinated paraffins, esters and sulphurized fats. EP oils can be either mineral or synthetic. EP oils also have viscosity grades between 68 and 1500, based on the ISO grading system.
Rust and oxidation preventive oils, also called R&O oils, have special rust and oxidation inhibitors included. These inhibitors include chemicals such as esters and organic acids. R&O oils are largely mineral oils and have a viscosity between 32 and 320, according to the ISO viscosity grading system.
Compounded gear oils contain a variety of compounds to give them properties similar to the other types of gear oil. As a result, compounded gear oils contain rust and oxidation inhibitors (which give them the properties of R&O oils) as well and demulsifiers (which keep certain chemicals separate and give compounded oils the same properties as EP oils). Compounded gear oils are used mainly in high-performance gears that generate a lot of heat and pressure. They are mineral based and have a viscosity between 460 and 1000.
Synthetic oils are gear oils that are not mineral based, but are composed of chemicals such as polyalphaolefins (PAO), esters and polyglycols. They are designed to withstand the most extreme pressures and temperatures. They have the properties of all of the aforementioned gear oils as well as a few other additives to make them suitable for their intended use. The viscosity of synthetic oils is between 36 and 320.
