Modern automatic transmission fluids typically contain a wide variety of chemical compounds intended to provide the required properties of a particular automatic transmission fluid specification. Most automatic transmission fluids contain some combination of additives that improve lubricating qualities, such as anti-wear additives, rust and corrosion inhibitors, detergents, dispersants and surfactants (which protect and clean metal surfaces); kinematic viscosity and viscosity index improvers and modifiers, seal swell additives and agents (which extend the rotational speed range and temperature range of the additives’ application); anti-foam additives and anti-oxidation compounds to inhibit oxidation and “boil-off (which extends the life of the additives’ application); cold-flow improvers, high-temperature thickeners, gasket conditioners, pour point depressant and petroleum dye. All automatic transmission fluids contain friction modifiers.
There are many specifications for automatic transmission fluids, such as the DEXRON and MERCON series, and the vehicle manufacturer will identify the automatic transmission fluid specification appropriate for each vehicle. The vehicle’s owner’s manual will typically list the automatic transmission fluid specification(s) that are recommended by the manufacturer.
Automatic transmission fluids have many performance-enhancing chemicals added to the fluid to meet the demands of each transmission. Some automatic transmission fluids specifications are open to competing brands, such as the common DEXRON specification, where different manufacturers use different chemicals to meet the same performance specification. These products are sold under license from the OEM responsible for establishing the specification. Some vehicle manufacturers will require “genuine” or Original Equipment Manufacturer (OEM) automatic transmission fluid. Most automatic transmission fluid formulations are open 3rd party licensing, and certification by the automobile manufacturer.
Each manufacturer has specific automatic transmission fluid requirements. Incorrect transmission fluid may result in transmission malfunction or severe damage.
Many vehicles today require a vehicle specific transmission fluid. Most of these today are synthetic transmission fluids. There are several different synthetic transmission fluids on the market today. Even though some vehicle manufactures require their own fluid the aftermarket fluids will work in most of these. You can run into problems if you use the wrong fluid or a cheap brand in modern vehicles. After a transmission repair or a transmission rebuild a qualified transmission repair professional will use the correct fluid for your specific automatic transmission.