page_title: Automatic transmission fluid
section_title: Sealed Transmissions
hierarchical_section_title: Automatic transmission fluid / "Lifetime" Fluids / Sealed Transmissions
caption_attribution_description: English: Umbrella Style Automatic Transmission Air Breathing Suppressor (TABS) 2017 Chevrolet Bolt EV. Extends ATF life.
context_page_description: Automatic transmission fluid is a kind of transmission fluid used in vehicles with self-shifting or 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 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-assisted steering systems, as a lubricant in some 4WD transfer cases, and in some modern manual transmissions.
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. Transmission manufacturers now use smaller, remote mounted, breather vents specially designed to keep out water, but allow a small amount of air movement through the breather as necessary.
caption: Umbrella style transmission breather to prevent water ingestion
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