Purpose of Transmission Fluid

• Transmission fluids work as a lubricant for the moving parts inside a transmission as well as a coolant. As the transmission fluid moves through the transmission, it also picks up metal particles and other contaminants from the transmission. As the fluid returns to the transmission pan, these particles are removed by the transmission filter.
  
  

Impact of New Transmission Fluid

• As the transmission fluid is exposed to extreme heat, the fluid will lose its lubricating properties. Old transmission fluid will also contain small contaminants from the transmission that the filter is unable to pick up. By replacing the fluid, the transmission will be better protected from friction as a result of the improved lubrication and removal of contaminants.
  
  

Transmission Fluid Change Interval

• Opinions vary on how often transmission fluid needs to be changed. A good starting point is to follow the vehicle's owner's manual recommendations, which can be as much as every 100,000 miles. However, many experts recommend changing the fluid more often. "Popular Mechanics" recommends changing the fluid every 30,000 miles.