Should I drain and fill my transmission?

When it becomes contaminated, overheated, or worn, automatic transmission fluid (ATF) can change appearance and smell. If your fluid is no longer a pink or deep red color on the dipstick, but has turned to any shade of brown, it's likely time to drain and fill it. If the fluid smells "burnt" this is also a sign that it has been overheated and is due to be drained and filled.

What happens if you don't change your transmission fluid?

The fluid inside a transmission works to lubricate and cool the moving parts inside. It also transfers hydraulic energy to make your transmission function properly. If you don't change the fluid regularly, the fluid will eventually become contaminated and break down chemically. Once this happens, it won't protect the moving parts from wear the way it should. It may also cause malfunctions inside the transmission, and it can cause the transmission seals to degrade and leak. Ultimately, this will lead to reduced fuel efficiency and horsepower at best, and a transmission that fails prematurely at worst.

What is better, transmission flush or drain and fill?

A transmission flush is the most thorough method of replacing the hydraulic fluid in an automatic transmission. While a fluid drain and fill will allow the transmission itself to be drained of old automatic transmission fluid (ATF), it does not remove the old ATF from the torque converter or other components of the system (valve body, transmission cooler, lines, etc.). A transmission flush is the only method of replacing all of the ATF in the system. It should be noted, however, that use of the service is sometimes debated. That is due to the method that some transmission flush machines employ, using high pressure and harsh detergents that are thought to impair the function of clutch packs and polymer parts inside some transmissions. Some vehicle manufacturers specifically advise against transmission flushes in their vehicles.