What Does Transmission Fluid Do?

Transmission fluid is a lubricant formulated to protect a vehicle’s gears and clutch packs while enabling smooth, crisp shifts.  Without it, transmission gears would rapidly wear out or overheat, resulting in a short life for the for the transmission and a huge expense for the owner.

The basic work of a transmission is – transferring power from the engine to the wheels. It houses a complex assortment of gears, clutches, solenoids and other components that select the proper gear for the operating condition at hand. When you accelerate or pull a heavy load, a lower gear is used which provides more torque. As you pick up speed, a higher gear is used to reduce engine rpm which increases fuel efficiency.

Today’s transmissions are smaller and must manage higher horsepower and torque, while delivering smoother shifts with longer fluid-life recommendations. These modern designs also pack in an enormous number of gears, clutch packs and narrow oil passageways that require a steady supply of high-quality fluid to function. Transmissions used for hauling or towing are subjected to massive torque and increased heat, the number one enemy of any transmission.

Types of Transmissions

  • manual
  • automatic
  • continuously variable transmissions (CVT)
  • dual-clutch transmissions (DCT).



Properties of Automatic Transmission Fluid

The primary job of a lubricant: to create a fluid film between metal surfaces to prevent contact and reduce friction. This protects against wear and fight the damaging effects of extreme heat.

A good transmission fluid also excels at the following tasks:

  • Functions as a hydraulic fluid

Automatic transmissions use pressurized transmission fluid to change gears. This stressor can cause the oil to shear and lose viscosity.

  • Delivers the right frictional requirements

Engagement and disengagement of the clutch packs must happen flawlessly for optimum performance.

  • Protects gears from wear

Automatic transmissions contain a system of sun, planetary and ring gears that require a durable lubricant film to prevent metal-to-metal contact.

  • Fights heat

Automatic transmissions generate more heat than manual transmissions. Heat accelerates oxidation, the chemical breakdown of the lubricant. Oxidation leads to sludge and varnish, which can clog narrow oil passages and contribute to clutch glazing. Vehicles can begin to shift hard, jerk or hesitate.

Properties of Manual Transmission Fluid

Manual transmission fluid has fewer jobs to perform than automatic transmission fluid. Some manual transmissions work with or even require ATF. There are attributes where quality manual transmission fluids must excel, such as protecting soft metal (brass) synchronizers from corrosion.

 Does Transmission Fluid Need To Be Changed?

Yes. Over time, transmission fluid oxidizes and becomes contaminated with particles and sludge. Transmission fluid don’t need to be changed as frequently as motor oil, it needs to be checked regularly.

If the transmission fluid level is low or the fluid has started to break down, the vehicle may shift poorly. Running low on fluid can damage transmission components and lead to catastrophic failure or expensive repairs.

How Often Should Transmission Fluid Be Changed?

Depending on the type of transmission and the mechanical stresses it must endure it is often recommended to change transmission fluid every 30,000-150,000 miles.

Original equipment manufacturer (OEM) recommendations for how often to change automatic transmission fluid cover a wide mileage range, depending on year, make and model. Plus, if your driving habits are like most motorists and fall under the “severe” designation (towing, hauling, daily short trips less than 10 miles etc.), many OEMs recommend changing transmission fluid more frequently. Check the recommendations in the owner’s manual. 

No lubricant last forever and provide the protection the vehicle requires. Over time, lubricants deteriorate, especially if used under heavy loads, frequent starts and stops or daily short trips.

It’s a good idea to check a vehicle’s transmission fluid periodically to monitor fluid level and condition.

 Choosing The Right Transmission Fluid

Use your owner’s manual or use the AMSOIL Product Guide to find the right transmission fluid for a specific vehicle. AMSOIL Signature Series Synthetic Automatic Transmission Fluid and OE Synthetic Automatic Transmission Fluid Transmission Fluid are both recommended for most of the common ATF specs on the market.

Signature Series Synthetic Automatic Transmission Fluid (click-on)

Signature Series ATF (ATF, ATL) is our premium transmission fluid designed for hard-working vehicles that operate in severe service. It handles heat so well, you can confidently double your vehicle manufacturer’s severe-service drain interval with guaranteed AMSOIL protection. It withstands the rigors of heavy towing, elevated temperatures and challenging terrain, and remains fluid in sub-zero temperatures. Signature Series ATF provides reserve protection for vehicles that endure heavy use and abuse.

OE Synthetic Automatic Transmission Fluid (click-on)

OE ATF (OTF, OTL) provides passenger car/light-truck transmissions excellent wear protection, sludge resistance and extreme-temperature performance throughout original equipment manufacturer (OEM)-recommended drain intervals. It provides excellent cold weather performance, guards against leaks and promotes smooth, shudder free shifts. OE Synthetic ATF is perfect for your daily commuter.

AMSOIL Synthetic CVT Fluid (click-on)

CVT stands for Continuously Variable Transmission. A CVT transmission uses a pair of variable-diameter pulleys and a belt/chain to provide unlimited gear ratios, enabling the vehicle to smoothly adjust to the optimal gear ratio in real time. CVTs require a unique transmission fluid with specialized frictional characteristics designed to ensure the belt or chain remains in contact with the pulleys without slipping. AMSOIL Synthetic CVT Fluid (CVT) provides outstanding metal-to-metal frictional properties and excellent protection and performance for CVTs throughout vehicle manufacturer-recommended drain intervals. In elevated heat, Synthetic CVT Fluid’s thermally stable formulation guards against the harmful effects of thermal breakdown. It resists the formation of varnish that can threaten transmission performance and life.

 AMSOIL 100% Synthetic DCT Fluid (click-on)

Dual-clutch transmissions (DCTs) are automatic transmissions based on the architecture of manual transmissions. The complex system essentially consists of two manual transmissions in the same housing. As one clutch is engaged, the other readies the next appropriate gear, minimizing the interruption of power and improving performance and efficiency. A specially formulated fluid is required to maintain the high-performance output of these advanced transmissions. AMSOIL 100% Synthetic DCT Fluid (DCT) is designed to protect high-tech dual-clutch transmissions during the most intense, high-heat operating conditions. It provides the fast, smooth shifts drivers expect. AMSOIL Synthetic DCT Fluid resists the extreme heat in today’s hightemperature DCTs to provide complete protection for gears, bearings and other vital parts. Its high film strength and anti-wear/extreme-pressure additives are specifically designed to protect the metal surfaces of DCTs.