What is the role an automatic transmission fluid?
An automatic transmission is a hydraulically-controlled gearbox requiring special fluid for its operation. The role of the fluid is to lubricate the internal, moving parts of the transmission, as well to transmit the power from the engine to the gearbox. The fluid ensures execution of the selected gearbox mode (forward, reverse, park, etc.) and gear change while driving.
How is the fluid changed?
It is important that an automatic transmission fluid be of the right class and that it be clean. Small contaminants, such as metal chips and other particulates get into the fluid while an automatic transmission is in operation. Not all of them are blocked by the filter.
With time, the fluid becomes contaminated and requires changing. This is done by unscrewing and removing the transmission fluid pan, removing the fluid contained in it, and, following screwing the pan back into place, pouring new fluid in. A good idea is to check the seal of the pan for potential leaks and change it, if necessary. Frequently, a new seal comes with the fluid filter set, as the filter requires changing together with the fluid.
After pouring in a new fluid of the classification suitable for a given car, and after checking its level, a test drive must be performed in order to check if the transmission operates properly and ensure that it is free from any leaks. After the test drive the fluid level should be checked again.
What to keep in mind
A failure to change the fluid may result in wrong operation of the transmission, resulting in gears being switched in the wrong moment or not being switched at all.
In extreme cases, the transmission may be damaged altogether. ATF or Automatic Transmission Fluid should be changed every 30 or 60 thousand kilometres. Some manufacturers recommend first change after as many as 100 thousand kilometres."