What's Involved in a Transmission Flush Mar 30, 2016 by Cedric (Driver Weekly)

Almost every single mechanic will suggest you flush your transmission at some point. While you know that you have to keep an eye on your transmission fluid levels, most people don’t necessarily think about flushing the system until their mechanic brings it up. However, your vehicle’s maintenance schedule should include a transmission flush at some point. This is considered necessary preventative maintenance for your vehicle.

The Basics

Before getting into the specifics of a transmission flush and how it works, you should understand the basic idea. In short, the mechanic removes all the oil within the transmission. They then run new oil, possibly with cleaning solutions, through the transmission using a special machine. This pushes out the sludge and grime within the transmission. After running this new solution through the transmission, the mechanic replaces the fluid with fresh oil.

The Details

The pumps responsible for flushing out the transmission oil are connected to the cooler lines of the transmission. The new fluid is pumped in at the same time the old fluid is removed. The flushing process can clean the cooling lines, as well as the cooler and converter, along with other parts. Ideally, the flushing process removes every single bit of sludge and debris and the old oil in the transmission is replaced with new oil that can perform better.

Fluid Flushes vs. Changes

Mechanics that endorse transmission flushes point out that a fluid change is just a temporary measure that doesn’t do a thorough job. Transmission flushes will exchange all the oil within the transmission while a change will just replace some of it. Some fluid, for example, remains stored within the torque converter. Since some of the old fluid remains after a change, it can quickly contaminate the new oil. Additionally, the change doesn’t remove deposits and obstructions that build up over time.

The Debate

In the past, most automakers and mechanics agreed that transmission flushes were necessary. Today, however, there is a great deal of debate. Some say that it is still essential to ensure that your vehicle runs properly while others say it can be damaging. On the other hand, critics claim the flushing equipment can cause damage. They say that it is possible that the gunk you flush out of the system won’t be removed completely; instead, it may become lodged somewhere else, leading to future issues. Others believe that the flushing process may bend or weaken the seals and valves, creating a potential mechanical issue. However, those who support transmission flushes are still in the majority. They point out the process’ ability to remove residue and other debris from the engine still seems to improve performance and durability.


The exact intervals for flushing the fluid will vary based on transmission type and who you ask. In most cases, your maintenance schedule for an automatic transmission will recommend a flush every 100,000 miles or 150,000 miles. Many mechanics, however, say it should be every 50,000 miles. To figure out if you are due for a transmission flush, consult your service schedule and talk to your mechanic. A transmission flush still seems like an effective way to get the most out of your transmission and maintain your car’s performance.


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