page_title: DEXRON
section_title: Sealed Transmissions
hierarchical_section_title: DEXRON / GM "Lifetime" ATF / Sealed Transmissions
caption_attribution_description: English: Umbrella Style Automatic Transmission Air Breathing Suppressor (TABS) 2017 Chevrolet Bolt EV. Extends ATF life.
context_page_description: DEXRON is the trade name for a group of technical specifications of automatic transmission fluid created by General Motors. The name is a registered trademark of GM, which licenses the name and specifications to companies which manufacture the fluid and sell it under their own brand names. Not all Dexron fluids are licensed for reselling under another brand name. All licensed Dexron fluids must have a license number that begins with the letters B through J. If no license number or "Dexron Approved" logo is found on the container, the fluid may not be GM approved and the fluid cannot be guaranteed to meet GM specifications. GM, like many automobile manufacturers, uses transmissions sourced from other suppliers or transmission manufacturers around the world; these transmissions are not manufactured by GM. Many of these automatic transmissions use unique fluids that might not be shown on this page.
  Originally the DEXRON name was associated exclusively with automatic transmission fluids, later GM released DEXRON gear oils and other lubricants under the DEXRON brand.
context_section_description: 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:
  The Dipstick Tube. Any transmission with a dipstick tube has the potential to let additional oxygen into the transmission through a dipstick that is not fully seated in the tube, or dipstick tube plug that is not fully seated. Even the process of checking the fluid level with a dipstick can allow additional oxygen and dirt into the transmission. Many modern transmissions do not have a dipstick, they have sealed transmission fluid level check plugs instead. By removing the traditional dipstick, the transmission manufacturer has also removed a potential entry point for oxygen; this reduces the potential for fluid oxidation. A sealed transmission will typically have longer transmission fluid life than a non-sealed transmission.
  The Transmission Vent. Transmissions need vents to compensate for internal air pressure changes that occur with fluctuating fluid temperatures and fluctuating fluid levels during transmission operation. Without those vents, pressure could build resulting in seal and gasket leaks. Before the use of better quality base oil in ATF in the late 1990s, some older transmission breather vents contained a Transmission Air Breathing Suppressor (TABS) valve to prevent oxygen and water ingestion into their transmissions. Oxygen reacts with high temperature transmission fluid and can cause oxidation, rust, and corrosion. Automatic transmission fluids using lower quality base oil oxidized more easily than fluids using higher quality base oils. GM, and other transmission manufacturers now use smaller, remote mounted, breather vents specially designed to keep out water, but allow the a small amount of air movement through the breather as necessary.
caption: GM Umbrella style transmission breather to prevent water ingestion
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