Automatic transmission fluid: types and maintenance of car transmissions

Even automatic transmissions require proper maintenance, and one of the key elements is the lubricating oil, or ATF (Automatic Transmission Fluid). This fluid doesn’t just lubricate, it also cools, cleans, and transmits power within the transmission. Over time, its properties degrade, making it necessary to replace it periodically in the workshop, according to the manufacturer's guidelines. Neglecting this aspect can compromise the lifespan and efficiency of the transmission.

To better understand the importance of the fluid, it helps to know the main types of automatic transmissions. Traditional automatic transmissions (AT) use a torque converter and planetary gears, offering robustness and smooth gear changes. There are 5–6-speed AT transmissions, more common in older vehicles, and more modern 6–7–8–9–10-speed transmissions, which offer greater efficiency, improved performance, and lower fuel consumption. CVTs (Continuously Variable Transmissions) don’t have fixed gear ratios; instead, they vary progressively using a belt (b-CVT) or chain (c-CVT), ensuring smooth, jerk-free driving. Lastly, dual-clutch transmissions (DCT) combine the efficiency of a manual gearbox with the convenience of an automatic, using two separate clutches to alternately manage even and odd gears, ensuring fast and precise gear shifts.

Knowing these differences is the first step toward conscious maintenance and ensuring your car delivers optimal and long-lasting performance.

Yes, changing the fluid in automatic transmissions is essential to ensure the proper functioning and longevity of the gearbox. Over time, ATF degrades due to heat, friction, and residues generated during operation. Worn-out fluid loses its lubricating and cooling properties, increasing the risk of slipping, erratic shifting, and damage to internal components. Replacing the fluid as per the manufacturer’s guidelines helps maintain optimal performance, reduces the risk of costly breakdowns, and contributes to the longevity of the transmission.

While fluids for manual and automatic transmissions share some functions, they also have distinct characteristics. In manual transmissions, the lubricant mainly reduces friction between gears, protects against wear and extreme pressures (EP) and dissipates heat generated during operation. Its role is primarily mechanical and passive.

In automatic transmissions, the lubricating fluid - ATF - not only performs those basic functions but also plays critical roles in system operation. ATF actively transmits power through hydraulic systems, controls the clutch and torque converter, and must ensure thermal stability, compatibility with synthetic materials (like seals) and consistent viscosity even at varying temperatures. Moreover, the formulations differ significantly depending on whether the transmission is AT, CVT, or DCT, requiring specific fluids for each type.