Automatic transmission fluid: What’s happening

Several months ago, I wrote about the changes in engine oil formulation. While the hobby has now generally digested the change to GF-4 oils, the auto and lubricants industries are hard at work on more changes, namely GF-5, to come in a couple of years.

Changes in lubricant specifications are not limited to just engine oils — automatic transmission fluid (ATF) is also undergoing its own transformation. When automatic transmissions first entered the marketplace on a regular basis, a single ATF meeting the requirements of the American manufacturers was the norm. General Motors called its ATF Dexron II and Ford’s specified fluid was labeled Mercon.

There was no change from 1949 through the late 1980s except for Ford. It required Type F in its automatics between 1961 and ’81. The late 1980s saw the introduction of Dexron-III/Mercon that posed no concern for car collectors because the new-specification ATF was backward compatible.

During the last two decades, there have been significant changes in automatic transmission design — more speeds, computer controls and more. In the quest to improve efficiency and economy, even more changes are on the horizon. These goals and the changes in transmissions have required changes in ATF. No longer is one specification applicable to all, as each auto manufacturer is developing its own ATF specifications to fit the specific needs of its own transmission. As a result, the license granted to lubricant manufacturers to produce Dexron-III/Mercon was terminated in June 2007.

This 1956 Cadillac Hydra-Matic automatic transmission will
operate on the new Dexron-IV ATF.

GM introduced Dexron-IV in 2005 for its 2006 models. Ford unveiled Mercon LV in 2007 and also has Mercon V for most pre-2008 models and Mercon SP for vehicles with six-speed transmissions. Chrysler has ATF+4 for its cars and the foreign manufacturers have theirs.

The primary difference between the new ATF lubricants and their predecessors is their viscosity. The new fluids are lower viscosity; their kinematic viscosity is typically on the order of 6 centiStoke (cSt) at 100 degrees C, while the older fluids are in the range of 7.0 to 7.5 cSt (heavier) at 100 degrees C. The lower viscosity helps improve low temperature performance and reduces friction for potential improvements in fuel economy. The additive mix in the newest fluids also offers improved oxidation stability, shear stability and friction durability to provide more consistent shift performance over the life of the fluid.

What does this mean for collector car owners?

The good news is that all the new ATF lubricants are backward compatible. That is, Dexron-IV can be used in all GM transmissions back to the beginning. The same is true for Chrysler’s ATF+4 for all prior Chrysler transmissions unless Dexron was specified, and Mercon V for Ford transmissions. The only exception is the 1961 to ’81 Ford transmissions that require Type F fluid.

Some lubricant companies, other than the car manufacturers, produce an ATF that meets multiple performance standards. Read the label carefully if you are using any of these fluids.
William C. “Bill” Anderson, P.E., has been involved with the automotive hobby for more than 30 years with experience ranging from hot rods, to sports cars, to sports car racing, and to restoration of vehicles from the 1930s through the `80s. He is an author, magazine editor, car show judge and professional engineer. A member of several car clubs and a leader in some, through Anderson Automotive Enterprises he restores and appraises cars.


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