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Transmission Flush Information

Everything you need to know about a transmission flush

What is a Transmission Flush?

► Should I Have My Transmission Flushed?

► Do-it-yourself Transmission Flush

► Should I Have My Transmission Flushed?

► Do-it-yourself Transmission Flush

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What is a Transmission Flush

Things you should know about a transmission flush:

» A transmission fluid flush is different from a fluid and filter change.
» A fluid flush will not repair an internal transmission problem.
» A fluid flush is a preventative maintenance procedure, not a cure all solution.
» A flush is not recommended for certain high mileage vehicles.
» A transmission flush is typically performed using a specialized flush machine.
» A transmission flush can be performed (DIY) using the transmission’s pump without a flush machine.

A transmission flush is a process in which the fluid in an automatic transmission is flushed out of the transmission and replaced with new ATF.  The flushing process, when done correctly, replaces nearly 100% of the old fluid with new fluid, including fluid in the torque converter and oil cooler lines.

IMPORTANT – PLEASE READ CAREFULLY: A pressurized transmission flush is not recommended for high mileage vehicles that have not been flushed previously. For these vehicles, the recommended service is a fluid and filter change.

Should I Have My Transmission Pressure Flushed?

As expected, the industry professionals who provide transmission flushes in their shops are proponents of the service while the non-flushing shops are typically against it.  We’ll do our best to sort through the rhetoric and provide you with the information you need to make an informed decision.

The debate as to the effectiveness and safety of a transmission flush continues among industry professionals. Some transmission experts give a thumbs up to flushing while others are completely against it.

Transmission Fluid Flush (Using Pressure Machine) – The Pros and Cons

The #1 benefit of a fluid flush, versus just a standard fluid/filter change is that nearly all the fluid (normally between 10 and 12 quarts) is flushed from the transmission and replaced with clean fresh fluid.

In this process, metal shavings, buildup and debris is also flushed from the transmission, torque converter and oil cooler lines, which is also a good thing.  Clean ATF insures the transmission is well lubricated and helps keep the tranny cool.

Is a transmission flush safe?

Anyone familiar with the subject of a pressure-machine transmission flush has undoubtedly heard stories from car owners about how a flush damaged their transmission or caused it to fail not too long after.  While some of these stories may be accurate, others are questionable or coincidental.

As mentioned at the beginning of this knowledge article, a transmission flush can be performed by a repair shop using a pressure flush machine or as a DIY project using the transmission’s internal pump to flush the old fluid out and the new fluid in.

In almost every case, when a vehicle owner states that his or her transmission failed shortly after a flush was performed the flush was done using a high-pressure flush machine at a repair facility. Here’s why:

A transmission flush machine uses high pressure along with a cleaning agent to flush the old fluid out of the transmission while simultaneously cleaning the internal parts.  During this process, the high-pressure cleaning does such a thorough job that it dislodges dirt and debris that the transmission’s internal pump is not strong enough to do.

If, while being flushed through the transmission, a piece of debris becomes lodged in a more crucial are of the transmission it can cause problems, even catastrophic transmission failure.  High-pressure flushing machines can also blow out internal seals in high-mileage transmissions.

NOTE: High mileage vehicles that have not routinely had transmission flushes performed are at the greatest risk of damage resulting from a high-pressure flush.

TIP: For high-mileage vehicles that have not routinely been flushed, A DIY flush using the transmission’s oil pump or a fluid and filter change is the appropriate service.

Where to have your transmission flushed

Many, but not all, transmission repair shops and automobile dealership service centers offer a transmission fluid flush service.

Do-it-Yourself Automatic Transmission Flush


Parts / Supplies / Tools Needed:

> Automatic Transmission Fluid
> Floor Jack & Jack Stands or Ramps
> Screwdriver, Ratchet and Socket Set
> Wheel Chock or Wooden Block
> Drain Pan
> Long Neck “skinny” Funnel
> Shop Rags or Paper Towels


Before flushing your transmission pull the dipstick and look closely at the fluid.  If the fluid is dark and has a burnt odor, atransmission flush is not recommended.  The recommended service is a fluid and filter change.


1) Start the engine and allow it to warm up to normal operating temperature and then shut it off. Place a wheel chock (or wooden block) behind one of the rear tires.

Raise the front of the vehicle with a floor jack. Position jack stands securely under the vehicle. Slowly lower the floor jack until the entire weight of the vehicle rests on the jack stands. Push on one corner of the vehicle to check stability of jack stands – the vehicle should not move.

Or, drive the front of the vehicle onto ramps.

2) Locate the two transmission oil cooler lines. These lines run from the transmission or transaxle to the radiator. One line carries hot ATF from the transmission to the radiator (transmission oil cooler) and the other line carries the cooled fluid back to the transmission.

Disconnect the lower transmission oil cooler line where it enters the radiator. Position the drain pan to catch the fluid coming out of the line.

3) From underneath the hood, pull the transmission dipstick out of the dipstick/fill tube and insert a long skinny funnel into the fill tube.


Note: If you do not have a long skinny funnel that will fit into the dipstick tube you can use a short funnel with a small diameter hose or tube extension.

The reason for using a longer funnel or a short funnel with an extension hose is that it makes it easier to keep the funnel filled with fluid during the flush.

4) Now, remove the caps from 9 quarts of transmission fluid and position the containers in close proximity to the funnel that you’ve inserted into the dipstick tube because once you start the engine you will continuously poor all 9 quarts into the transmission one quart immediately after the other. As you are pouring the new fluid into the transmission, the old fluid is being pumped out of the transmission into the drain bucket.

5) Start the engine and pour all 9 quarts of fluid into the transmission through the funnel trying not to allow the funnel to run dry before beginning to add the next quart. When all 9 quarts have been added, shut the engine off.

6) Reconnect the transmission oil cooler line. Now, back up on top, remove the funnel from the dipstick/fill tube and insert the dipstick. Be sure the dipstick is pushed all the way down into the tube.

7) Now start the engine while the vehicle is still raised and check for leaks. If no leaks are present, shut the engine off and then lower the vehicle.

8) With the vehicle sitting on level ground, start the engine and allow it to warm up to normal operating temperature. Once warm, depress the brake pedal and move the shifter through all gears (pausing for a couple of seconds between each shift) before returning the shifter to the Park “P” position.

9) Check fluid level. With the engine still on and at idle, pull the transmission dipstick and check the fluid level. If it shows full, (or in the full range), wipe the dipstick clean then reinsert it back into the tube. Check fluid level a second time to confirm the reading. If it shows full a second time, you are done. If the fluid level is low, add no more than 1/3 quart of fluid – then recheck. Repeat this process, adding less fluid each time, until the dipstick reads full, or in the full range. Do NOT overfill.


Note: Most automatic transmissions do not have a drain plug. So, if you accidently overfill the transmission with fluid, remove one of the oil cooler lines where it enters the radiator to allow some fluid to drain out. Or, if you have a small hand pump and a long small diameter hose you can pump fluid out of the transmission through the dipstick/fill tube.

This concludes the DIY Automatic Transmission Flush Procedures

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