Automatic transmission oil: functions, types, replacement

Automatic transmission is one of the most loaded and at the same time the most expensive to repair car components. But, accustomed to ease of use, many motorists simply forget that automatic transmission, like all other parts of the machine, requires compliance with certain rules of operation and maintenance.

Automatic transmission resource

Despite the strength and reliability, the automatic transmission can fail, but it can also serve as much as the whole car without problems. In order not to have to carry out automatic transmission repairs ahead of time, it is necessary to follow the operating rules and conduct maintenance.

The resource of the automatic box depends on the wear of the parts, which is difficult to notice at the very beginning, but it looks very sad in the “neglected form of the disease”. And you can accelerate wear not only in the harsh working conditions of the car, but also in an untimely oil change.

The automatic transmission resource depends primarily on the wear of the friction clutches (rings, of which there are several blocks), steel and covered with paper linings. This process depends on the mode and style of driving, the absence of constant loads and timely oil changes, because it protects the rubbing vapors from overheating, carbonization and breakage.

Oil function

Automatic transmission fluid (Automatic Transmission Fluid, ATF or ATP) performs several functions at once, some of which are opposite in nature.

  • During operation, the gears heat up and the oil removes heat from them. The oil itself is cooled in an automatic transmission fluid radiator, which is installed either separately or in a block with an engine cooling radiator.
  • Cleaning up. The oil removes the products of wear of parts and leaves them on the filter (similar to engine oil).
  • Antifriction grease. All rubbing parts must be properly poured with oil to minimize wear of metal parts.
  • Torque transmission. In a torque converter, oil is used precisely for this purpose: it transfers the torque from the engine flywheel to the gearbox.
  • Corrosion protection. Like any other oil, the liquid protects the automatic transmission parts from moisture.
  • Friction clutch. The oil must provide traction, falling on friction pairs.

The operating conditions of ATP fluid are even more stringent than that of motor oil, and the requirements for it are much higher. Some functions (anti-friction coating on metal and improved adhesion of special friction linings) are opposite in nature, and high-quality oil copes with them thanks to correctly selected additives.

The composition of the oil for the automatic transmission

ATP would be wrong to call oil in the truest sense of the word. However, it also performs lubrication functions, including, therefore, the term "oil" is used in everyday life most often.

Automatic transmission fluid consists of a basic base, which can be used crude oil or synthetic substances. Accordingly, the oils are divided into synthetic, semi-synthetic and mineral. The basis is 85-90% of the final product volume. View here for more info: too much transmission fluid

In addition to the base, a specially developed additive package is used (10-15% of the volume), on which, in fact, the properties of the oil depend. As a rule, the additive package of modern oils includes:

  • anti-foaming agents
  • corrosion inhibitors (protect metal parts)
  • antioxidants (protect the oil itself from premature oxidation)
  • dispersants (prevent solid particles from precipitating by holding them in oil),
  • friction modifiers
  • viscosity optimizers (do not allow the oil to thicken strongly at low temperatures),
  • substances that increase the wear resistance of rubbing nodes,
  • additives that increase the flash point of the oil,
  • protective components that prevent oil from affecting rubber parts (gaskets and seals).

In addition to the base and additives, dyes are also included in the oil. They are used to quickly distinguish  automatic transmission oil from other lubricants, as well as for the internal differentiation of oils of the same brand (different series may contain different dyes). The liquid after filling into the gearbox very quickly loses its bright color, becoming a standard light yellow-brown color.

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