Transmission Service: Refill or Flush?
Changing transmission fluid is as important as a basic oil change when it comes to maintaining a properly operating vehicle and thus avoiding a potentially serious transmission repair. There are two common methods that are used to change the fluid during a transmission service: "drain and refill" and "flush."
The descriptions below may help you understand the "why" and "when" each method might be recommended by your transmission service technician:
- "Flush"
The 'flush' method uses a special flushing machine that is connected in series to one of the fluid cooler lines. This flushing machine gradually pumps out the old fluid while replacing it with new at the same time while the engine is running. This machine allows the replacement of approximately 90-95% of the fluid at once.
- "Drain and Refill"
The 'drain and refill' method involves draining the fluid, either from the drain plug, or by removing the pan, and then refilling the transmission with new fluid. Many makes of vehicles also have a filter that should be replaced at the same time. The 'drain and refill' method only allows about 40%-50% of fluid to be changed at once, as a large portion of the fluid remains in the torque converter, valve body and other parts of the transmission, and therefore cannot be drained.
Which method is best?
As to which method is better remains a mostly opinion. Using a flush machine is obviously quicker and more efficient and it is successfully used in many auto shops. However, many mechanics advise that it is better to repeat a 'drain and refill' method a few times. Some vehicle manufacturers do not recommend using flush machines.
A general "rule of thumb": The "drain and refill" method is typically safer for high-mileage vehicles, while the "flush" method (if approved by the car manufacturer), might work well for low-mileage cars. Regardless of which method is used, the service should only be performed by a qualified auto technician in order to avoid a more serious transmission repair in the future.
Have questions about transmission service? Contact our ASE Certified Technicians at Clausen Automotive by calling (608) 221-8321 for more information. Since 1975, our family-owned auto shop has proudly served vehicle owners in Madison, WI, and the surrounding communities.
Changing transmission fluid is as important as a basic oil change when it comes to maintaining a properly operating vehicle and thus avoiding a potentially serious transmission repair. There are two common methods that are used to change the fluid during a transmission service: "drain and refill" and "flush."
The descriptions below may help you understand the "why" and "when" each method might be recommended by your transmission service technician:
- "Flush"
The 'flush' method uses a special flushing machine that is connected in series to one of the fluid cooler lines. This flushing machine gradually pumps out the old fluid while replacing it with new at the same time while the engine is running. This machine allows the replacement of approximately 90-95% of the fluid at once.
- "Drain and Refill"
The 'drain and refill' method involves draining the fluid, either from the drain plug, or by removing the pan, and then refilling the transmission with new fluid. Many makes of vehicles also have a filter that should be replaced at the same time. The 'drain and refill' method only allows about 40%-50% of fluid to be changed at once, as a large portion of the fluid remains in the torque converter, valve body and other parts of the transmission, and therefore cannot be drained.
Which method is best?
As to which method is better remains a mostly opinion. Using a flush machine is obviously quicker and more efficient and it is successfully used in many auto shops. However, many mechanics advise that it is better to repeat a 'drain and refill' method a few times. Some vehicle manufacturers do not recommend using flush machines.
A general "rule of thumb": The "drain and refill" method is typically safer for high-mileage vehicles, while the "flush" method (if approved by the car manufacturer), might work well for low-mileage cars. Regardless of which method is used, the service should only be performed by a qualified auto technician in order to avoid a more serious transmission repair in the future.
Have questions about transmission service? Contact our ASE Certified Technicians at Clausen Automotive by calling (608) 221-8321 for more information. Since 1975, our family-owned auto shop has proudly served vehicle owners in Madison, WI, and the surrounding communities.
