Transmission Lubricants, commonly referred to as ATF or (Automatic Transmission Fluid, are applicable not only in automatic transmission types, as the name suggests, but can be used in manual transmissions as well. This fluid is usually characterized by having a distinctive red or green tint in order to make it distinct from the other fluid types used in the engine of a motor vehicle. ATF requires the engine to be running in order to be checked by pulling its reservoir's dipstick.
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ATF is not only used in transmissions, however, but also as a hydraulic fluid or lubricant in some 4-Wheel-Drives and Power Steering Systems. This type of fluid has been optimized with the special needs of the transmission in mind. Things like valve operation, torque conversion, and the friction of the brake band are some of those important special needs kept in mind when the fluid was designed. The most common types of ATF will be composed of the fluid and some number of additives designed to increase the quality of lubrication it provides: there are anti-wear additives like rust and corrosion inhibitors, detergents, surfactants, and dispersants. More notable additives include seal swell agents, which allow for a greater range of safe rotational speeds and temperatures, anti foamers and compounds to prevent oxidation and boil off. There are even cold-flow additives, ones that thicken the compound at high temperatures, conditioners for the gasket, pour point depressant, and even a petroleum dye!