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Dexron is the trade name for a group of technical specifications of automatic transmission fluid created by General Motors (GM). The name is a registered trademark of GM, which licenses the name and specifications to external companies which manufacture the fluid and sell it under their own brands. GM has upgraded the Dexron specifications over the years; newer fluids are generally but not always backward compatible with previous Dexron fluids. The current fluid is Dexron-VI, introduced in 2005.
Originally the Dexron name was associated exclusively with automatic transmission fluids, but more recently[when?] GM has released Dexron-branded gear oils. The brand name is commonly mispronounced as "Dex-tron".
The original Dexron transmission fluid was introduced in 1968 as an improvement over the previous "Type-A, Suffix-A" fluid. Over the years, the original Dexron was supplanted by Dexron-II, Dexron-IIE, Dexron-III, and Dexron-VI, which is the current fluid. Because there are still applications for which Dexron-VI is either not suitable or not necessary, there remains a market for fluids meeting older Dexron specifications.
The original Dexron fluid, like its predecessor Type-A/Suffix-A, used sperm whale oil as a friction modifier. The U.S. Endangered Species Act banned the import of sperm whale oil, so Dexron fluid had to be reformulated.
Dexron-II was introduced in 1972 with alternative friction modifiers such as Jojoba oil. However, it made problems with corrosion-prone solder in GM's transmission fluid coolers and so had to be reformulated.
Corrosion inhibitors were added to Dexron-II to address the solder corrosion issue. The resultant fluid, released in 1975, was called Dexron-IID. However, the corrosion inhibitor made the new fluid hygroscopic to a problematic degree, and so had to be reformulated. Although the hygroscopicity was not a major problem in automatic transmissions, for which the fluid was originally intended, Dexron ATF:s were also used in other hydraulic systems, which is where the hygroscopicity was a problem.
Dexron-IIE was introduced in an effort to address the hygroscopicity problems with the previous IID fluid.[vague]
In 1993, GM released new Dexron-III fluid. It is generally backward-compatible with transmissions originally filled with earlier Dexron fluids or with Type-A/Suffix-A fluid.
The fluid specification for Dexron-VI was introduced in 2005,and was first used as the GM factory-fill automatic transmission fluid for model year 2006. All Dexron-III licenses expired permanently at the end of 2006, and GM now supports only Dexron-VI fluids for use in their automatic transmissions. Fluids asserted by their manufacturers to meet Dexron-III standards continue to be sold under abbreviated names such as Dex/Merc, but the licensing system no longer exists. These fluids are not regulated by GM. Dexron VI is of a slightly lower viscosity when new compared to the prior Dexron fluids (a maximum of 6.4 cSt at 100°C for Dexron VI and 7.5 cSt for Dexron III), but the allowed viscosity loss during use (from shearing of the ATF) is lower for Dexron VI, resulting in the same lowest allowed final viscosity for both Dexron III and VI (5.5 cSt). The intent of the lighter viscosity is to gain an incremental improvement in fuel economy by lessening parasitic drag in the transmission. Since Dexron VI is not allowed to thin out (lower its viscosity) as much as Dexron III during use, it requires the use of higher-quality, more shear-stable (thins less in use) base stocks (the base oils, to which additives are added to make ATF).