Dexron is the brand name of transmission fluid manufactured for General Motors vehicles; Dexron-II was released in the 1970s, and Dexron-III was released in the 1990s. Dexron-III is considered to be backward compatible with other versions of Dexron, meaning it can be substituted for Dexron-II and other older versions of the fluid. However neither version of the transmission fluid is currently manufactured or marketed, and the most current version, Dexron-VI, is used in a backward-compatible fashion with GM cars that require either Dexron-II or Dexron-III.
One of the biggest differences between Dexron-II and Dexron-III, aside from their different names and the different years in which they were developed, is the fact that Dexron-II was originally marketed with alternative ingredients such as jojoboa oil. This reflected the public trend toward "natural" ingredients that became popular in the 1970s. Subsequent versions of Dexron-II were released to compensate for the issues caused by the use of inferior ingredients in the original Dexron-II, including Dexron-IID and Dexron-IIE.
Only one version of Dexron-III was ever marketed after it hit the market in 1993, and it was replaced by Dexron-VI in 2005. Some replacements for Dexron-III may be available on the market today, but these products are not officially approved by the General Motors Company.