Automatic transmission fluid (ATF) is a type of hydraulic fluid used in vehicles with automatic transmissions. It is typically coloured red or green to distinguish it from motor oil and other fluids in the vehicle.
The fluid is optimized[1] for the special requirements of a transmission, such as valve operation, brake band friction, and the torque converter, as well as gear lubrication.
ATF is also used as a hydraulic fluid in some power steering systems, as a lubricant in some 4WD transfer cases, and in some modern manual transmissions.
Modern ATF consists of a base oil plus an additive package containing a wide variety of chemical compounds intended to provide the required properties of a particular ATF specification. Most ATFs contain some combination of additives that improve lubricating qualities,[2][3][4] 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"[5] (which extends the life of the additives' application); cold-flow improvers, high-temperature thickeners, gasket conditioners, pour point depressant and petroleum dye. All ATFs contain friction modifiers, except for those ATFs specified for some Ford transmissions and the John Deere J-21A specification;[6] the Ford ESP (or ESW) - M2C-33 F specification Type F ATF (Ford-O-Matic) and Ford ESP (or ESW) - M2C-33 G specification Type G ATF (1980s Ford Europe and Japan)[3] specifically excludes the addition of friction modifiers.[3] According to the same oil distributor, the M2C-33 G specification requires fluids which provide improved shear resistance and oxidation protection, better low-temperature fluidity, better EP (extreme pressure) properties and additional seal tests over and above M2C-33 F quality fluids.
Note that the friction modifier only means that the fluid sticks to the surface of the metal a little more strongly, and therefore only helps to prevent early wear. It would be required for Ford, BorgWarner to prove that their transmissions are somehow harmed by friction modifiers. In many countries, Ford has said that the modern Dex3 fluid is fine for the same transmissions that it says require the older standard.[citation needed]
There are many specifications for ATF, such as the General Motors (GM) DEXRON and the Ford MERCON series, and the vehicle manufacturer will identify the ATF specification appropriate for each vehicle. The vehicle's owner's manual will typically list the ATF 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 ATF 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) ATF. Most ATF formulations are open 3rd party licensing, and certification by the automobile manufacturer.
Each manufacturer has specific ATF requirements. Incorrect transmission fluid may result in transmission malfunction or severe damage, however this occurs where the viscosity is extremely different.[citation needed]
Synthetic ATF is available in modern OEM and aftermarket brands, offering better performance and service life for certain applications (such as frequent trailer towing).
The use of a lint-free white rag to wipe the dipstick on automatic transmissions is advised so that the color of the fluid can be checked. Dark brown or black ATF can be an indicator of a transmission problem, vehicle abuse, or fluid that has far exceeded its useful life. Over-used ATF often has reduced lubrication properties and abrasive friction materials (from clutches and brake bands) suspended in it; failure to replace such fluid will accelerate transmission wear and could eventually ruin an otherwise healthy transmission. However, color alone is not a completely reliable indication of the service life of ATF as most ATF products will darken with use. The manufacturer's recommended service interval is a more reliable measure of ATF life. In the absence of service or repair records, fluid color is a common means of gauging ATF service life.
CVTs and dual-clutch transmissions often use specialized fluids. Transfer cases and differentials in four-wheel-drive/all-wheel-drive vehicles sometimes require specialized fluids, such as Honda Dual Pump-II, Honda VTM-4, Jeep Quadra-Trac, etc.
The history of automatic transmission fluids parallels the history of automatic transmission technology. The world's first mass-produced automatic transmission, the Hydra-Matic 4-speed, was developed by General Motors (GM) for the 1940 model year. The Hydra-Matic transmission required a special lubricant GM called Transmission Fluid No. 1. for the Hydra-Matic Drive. This transmission fluid was only available at Oldsmobile, Pontiac, and Cadillac dealerships. Subsequent automatic transmission and fluid coupling technologies, and difficulties with fluids in cold and hot temperature extremes led to a need for longer lasting, higher quality transmission fluids. Additionally, a better system of automatic transmission fluid distribution and marketing was necessary for the long term success of the automatic transmission.
In 1949, GM released a new Type "A" fluid specification.[9][10] In an attempt to make GM automatic transmission fluid available at retailers and service garages everywhere. Every automatic transmission produced by any vehicle manufacturer used GM Type "A" transmission fluids in their transmissions from 1949-1958.
In 1959, Ford began releasing their own automatic transmission fluid specifications, see MERCON for more information. From 1958-1968 many vehicle manufacturers continued to use the next GM automatic transmission fluid specification, the Type "A" Suffix "A" fluid in their transmissions. In 1966, Chrysler began releasing their own automatic transmission fluid specifications, see Mopar ATF for more information. GM ATF was the same color as engine oil through 1967. Aftermarket ATF was available with red dye as an aid in fluid leak detection. Dexron (B) was the first GM ATF to require red dye.
In the 1940s, 1950s, 1960s, and early 1970s, ATF contained whale oil as a rust and corrosion inhibitor.[11] A moratorium on whale oil at that time prevented the continued production of older ATF such as the original 1967 DEXRON formulation (Type B), and the fluids which preceded it. Vintage GM (1940-1967), Ford (1951-1967, and Chrysler products (1953-1966) used GM Type A fluid or GM Type A Suffix A fluids; these fluids are no longer produced. GM recommends Dexron-VI fluid, Ford recommends Mercon V fluid, and Chrysler recommends ATF+4 fluids for vintage transmission use.
Through the late 1970s, Ford transmissions were factory filled with a fluid identified as ESW M2C33-F. To provide a fluid that would be available to the general public for service fill, oil companies and other than factory fill suppliers were allowed to develop fluids meeting the ESW M2C33-F specification and market these fluids under their own brand names but identified as Type F.
The second generation of transmission fluid was released in 1974 as the factory fill specification, ESW M2C138-CJ. This fluid was developed to modify the vehicle shifting characteristics and to provide considerable improvement in the oxidation resistance and anti-wear performance.
No service fluids were developed and for a short time, DEXRON fluids approved by General Motors were considered acceptable. With continuing changes and improvements in transmission design, a centrifugal lock-up torque converter clutch was introduced into the C5 transmission to smooth engine vibrations sensed by the occupant of the vehicle. An associated shudder problem forced the introduction of the factory fill specification ESP M2C166-H. Servicing transmissions with DEXRON fluids was unacceptable since not all DEXRON fluids were capable of eliminating the shudder phenomenon. The fluids that could be used were a subset of the DEXRON fluids. The advent of Type H as factory fill necessitated the development of a service fluid specification to match the performance expected from Type H. This resulted in the release of the MERCON specification in 1987.[12]
One major revision occurred in September 1992, when low-temperature viscosity requirements, volatility requirements, viscosity change limits after high-temperature exposure and improved oxidation limits were introduced. These changes raised the performance of MERCON fluids above ESP M2C166-H levels.
The development of modulating and continuous slipping clutch converters has prompted the need to develop the MERCON V specification. Included are requirements to verify the anti-wear capabilities and anti-shudder characteristics of the fluid.
The MERCON V specification was further modified some time prior to 2007 to make it backward-compatible with MERCON. Ford has / is terminating all license agreements for the manufacture and sale of MERCON in favor of MERCON V.[13]
Toyota continued using GM ATF, including Dexron (B) and Dexron-II(D) in most of their automatic transmissions until 2003. In 1988, Toyota began releasing their own automatic transmission fluid specifications, see Toyota ATF for more information.
In 1967, Ford produced the Type-F fluid specification. The Type-F specification was intended to produce a "lifetime" fluid which would never need to be changed. This was the first of many Ford "lifetime" fluids. The 1974 Ford Car Shop Manual reads "The automatic transmission is filled at the factory with "lifetime" fluid. If it is necessary to add or replace fluid, use only fluids which meet Ford Specification M2C33F. Many other transmission manufacturers have followed with their own "Lifetime" automatic transmission fluids".
To understand how a fluid can last a "lifetime", a study of the 1939 Chrysler Fluid Drive Fluid is helpful. The lesson learned by Chrysler with its fluid drives is applicable to modern automatic transmissions as well.[14] The November 1954 edition of Lubrication Magazine (Published by The Texas Company, later known as Texaco) featured a story called "Evolution of the Chrysler PowerFlite Automatic Transmission". This article described the fluid used in the 1939 Chrysler Fluid Drive and its subsequent revisions and enhancements through 1954.
The fluid drive fluid coupling is partially filled with Mopar Fluid Drive Fluid, a special highly refined straight mineral oil with a viscosity of about 185 SUS at 100°F., excellent inherent oxidation stability, high viscosity index (100), excellent ability to rapidly reject air, very low natural pour point (-25°F.), ability to adequately lubricate the pilot ball bearing and seal surface, and neutrality towards the seal bellows.
The fluid operates under almost ideal conditions in what is essentially a hermetically sealed case, the small amount of atmospheric oxygen initially present is removed by a harmless reaction with the fluid so as to leave a residual inert (nitrogen) atmosphere. As a consequence, it has not been necessary to drain and replace the fluid, and the level-check recommendation has been successively extended from the original 2,500 miles to 15,500 miles and finally to "never" - or the life of the car.
Since drains and level checks were not only unnecessary but frequently harmful (through the introduction of more air, and seal-destroying dirt) Chrysler eventually left off the tempting level inspection plugs. This mechanism is, therefore, one of the very few that are actually lubricated for the life of the car. There are now myriad examples of couplings that have operated well over 100,000 miles without any attention whatsoever and were still in perfect condition when the car was retired.
On European type cars, a "Lifetime" means 180,000 km or 112,000 miles as a lifetime of a vehicle or transmission. Service intervals of newer type cars are from 80,000 to 120,000 km which equals 50,000 to 75,000 miles. Flushing or refilling the fluid on lifetime filled transmissions require to use equipment to fill from below, engaging the transmissions torque converter or using an external pump.[15][16][17][18]
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Any automatic transmission fluid will last longer if the transmission case could be hermetically sealed, but transmissions typically have two potential entry points for air:
Any automatic transmission fluid will last longer if it comes from an unopened container
Lifetime automatic transmission fluids made from higher quality base oil and an additive package are more chemically stable, less reactive, and do not experience oxidation as easily as lower quality fluids made from lower quality base oil and an additive package. Therefore, higher quality transmission fluids can last a long time in normal driving conditions (Typically 100,000 miles (160,000 km) or more).
The definition of 'Lifetime Fluid" differs from transmission manufacturer to transmission manufacturer. Always consult the vehicle maintenance guide for the proper service interval for the fluid in your transmission and your driving conditions.
Chevrolet Colorado Example: According to the Scheduled Maintenance Guide of a 2018 Chevrolet Colorado with "Lifetime Fluid" could have two different fluid service intervals depending upon how the vehicle is driven:[22]
Under "Severe" driving conditions, replace automatic transmission fluid and filter every 45,000 mi (72,420 km)
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For over 70 years, the oil aftermarket has produced both licensed, and non-licensed, formulations of automatic transmission fluids (ATF).[23][24] Today, aftermarket fluids asserted by their manufacturers to be compatible for use in various brands of automatic transmissions continue to be sold under names such as Multi-Purpose and Multi-Vehicle fluids. Non-licensed fluid is typically less expensive; these fluids are not regulated or endorsed by the vehicle manufacturer for use in their transmissions. Vehicle manufacturer approved and licensed fluids must have the license number printed on the product information label of the container or on the container housing. Non-Licensed fluids do not show a license number. Make sure the fluid to be installed into a transmission matches the recommended fluid in the specifications section of the vehicle's owner's manual.
ATF which has been mislabeled, has misleading labeling, or is fraudulently bottled as another product is an ongoing problem. Some of these fluids have led to multiple transmission failures.[25] The three organizations shown below are trying to stop this problem in the United States.