What is a Transmission Flush?

Malcolm Tatum
Malcolm Tatum

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.

A qualified mechanic should perform a transmission flush.
A qualified mechanic should perform a transmission flush.

Fluid Drain

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.

A clutch, part of a transmission.
A clutch, part of a transmission.

Full Flush

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.

A transmission without the housing.
A transmission without the housing.

Possibility of Damage

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.

Professional Service Recommended

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.

In most cars and trucks, the transmission system has a fixed number of gears that can be used at various speeds.
In most cars and trucks, the transmission system has a fixed number of gears that can be used at various speeds.
Malcolm Tatum
Malcolm Tatum

After many years in the teleconferencing industry, Michael decided to embrace his passion for trivia, research, and writing by becoming a full-time freelance writer. Since then, he has contributed articles to a variety of print and online publications, including wiseGEEK, and his work has also appeared in poetry collections, devotional anthologies, and several newspapers. Malcolm’s other interests include collecting vinyl records, minor league baseball, and cycling.

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Discussion Comments


Should the transmission oil be changed in a 2008 Chrysler Sebring?


Are the concerns about having the gaskets not work as well valid? Is it maybe for more old cars? I have a Honda, so I don't think I need to worry about flushing the transmission, but we were thinking about doing it for my wife's Ford.


I think that my car needs a new transmission. It seems like it is having a hard time shifting every time that I go from first to second gear. It is having a hard time so I think it would be nice to get it checked out.


I don't know if I should get a new transmission or just try this first. Thanks for sharing. It's really helpful!


The mechanics had us watch as they did my transmission repair in Toronto. I learned so much.


We held off on buying Chevys for years and years and years, then we broke down and bought one recently. Damn thing has cost us several thousand. Chevy stinks. Hope they go bankrupt.


Never buy a chevy. They do run deep straight into the ground. As a mechanic for 20 years, I see more chevrolet/gmc products needing more major repairs than any other vehicle. Only buy a chevy if you like sitting in a garage waiting for repairs to be done.


Thanks for the correct info! I just had mine done my Kia Dealer and Then I read it could "blow out my seals". My regular mechanic, whom I trust, suggested it since I told him I want my car to go to 200,000 without major repairs.


About transmission flushing: it can void your warranty. There are no automobile manufacturers that recommend flushing, but they do recommend draining. Flushing is pushed by the manufacturers of flushing equipment and stations that charge $100 for what should cost no more than an oil change.


don't buy dodge. Any experienced car buy knows to dodge a dodge, they are unreliable and notorious for problems all across the board. they're like a dollar store car.


sounds like a broken motor mount. the smell of burning could be your brakes because the vibration increases. And the smell of gas and burning usually means you're about blow up. I'd have it towed to a mechanic.


96 Dodge Intrepid shakes or vibrates when engine is turned on, worse when brakes are applied for any length of time. Gasoline and burning smell.

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