What is a Transmission Flush?

A transmission flush is a process that clears old fluid from the transmission of a motor vehicle and replaces it with new fluid. This process also helps to remove residue from the converters, coolers and cooler lines. There is some difference of opinion about whether transmission flushes are necessary. Some people say that conducting regular transmission flushes will enhance the function and extend the life of the vehicle's transmission. Others say that transmission flushes are unnecessary and can damage the vehicle's transmission valves and seals.

In a simple draining of old transmission fluid, a drain plug in the transmission is removed, and the fluid is allowed to flow out and accumulate in a pan. Although this process makes it possible to remove the majority of the older fluid, it does not thoroughly cleanse the system. The result is that there still is a bit of older fluid and residue in the system. When this is the case, the old fluid will mix with the new fluid, which might reduce the effectiveness of the new fluid.

With a transmission flush, more of the old fluid is removed, and the overall transmission system is cleansed. This means that there is less residue to contaminate and weaken the new fluid. In some cases, a special transmission flush fluid is used to help clean the system before the new transmission fluid is added. The presence of fresh transmission fluid means that less stress is placed on the transmission itself, which can prolong the life of the transmission.

Some people believe that a transmission flush might blow out the valves and seals on the transmission, but this is possible only when high pressure is used to force fluid backward through the transmission system. In most cases, however, a transmission flush does not rely on pressure to flush out the residue of the old fluid. Instead, the transmission's pump is used to gently introduce the new fluid into the system. This means that rather than applying pressure that could damage the transmission, simple displacement is used to rid the system of the majority of the old fluid.

Although it is possible to buy transmission flush machines for home use, most experts say that it is better to have a qualified mechanic perform the flush. A transmission flush typically costs a little more than simply draining and replacing the fluid, but the investment can mean a smoother operation for the transmission. It also could minimize the chances of having to replace the entire transmission during the life of the vehicle.