Virtually all motor-powered vehicles have transmissions and those transmissions are filled with lots of fluid. The fluid gets dirty in time and can even accumulate sediment that can damage the transmission.
Draining the fluid from a transmission and then refilling it is something most car owners can do for themselves, if they wish. However, a large amount of old fluid will remain in the system because only the transmission fluid pan will be drained. Draining and refilling the fluid multiple times will reduce the percentage of dirty fluid left in the system.
Flushing the fluid from the transmission system entirely has the advantage of exchanging a greater amount of fluid than a simple drain and fill. However, flushing takes longer to perform, and manufacturers recommend that this service be performed by professionals.
In general, car manufacturers recommend new transmission fluid between every 40,000 to 100,000 miles traveled. This prolongs the life of the transmission and keeps the system running efficiently.
