What to Know About Changing Transmission Fluid

March 20, 2025

6 min read

March 20, 2025

6 min read

Transmission fluid is oil that lubricates the car’s gearbox. In a manual transmission, it is simply a lubricant. In an automatic transmission, transmission fluid pulls double duty. It lubricates the gears and also serves as the hydraulic fluid that tells the transmission when to shift and sends power from the engine to the wheels.

The transmission fluid is critical to your transmission working right. All kinds of issues can crop up if you don’t change it regularly.

See our video and article - opens in new window or tab. for a complete step-by-step guide to changing transmission fluid.

What Transmission Fluid Does

A pickup truck transmission with the pan removed. — Clean transmission fluid is essential. This truck is overdue for a fluid change.

In automatic transmissions, transmission fluid provides the hydraulic pressure that makes the whole transmission work. A separate clutch and gear lever control a manual gearbox to shift between gears, and in an automatic system, the clutches and shifting mechanism are inside the transmission itself.

Transmission fluid provides friction between the internal clutches to allow the gears to engage and disengage, flows through a valve body that controls the shifts, and provides hydraulic pressure in the torque converter. The torque converter is simply a big fluid coupling that engages and disengages the engine from the transmission.

When to Change Your Transmission Fluid

A mechanic draining transmission fluid by tilting the transmission pan forward after unbolting it. — Draining automatic transmission fluid can be messy.

In most vehicles, you should change the transmission fluid on a regular schedule like engine oil. But transmission fluid doesn’t need to be changed as often. As a general rule, you can expect transmission fluid to last between 30,000 and 60,000 miles.

If you often tow heavy loads, live somewhere with extreme weather, go off-roading, or run a track day or two every weekend, transmission fluid will wear out faster.

Can you change your own transmission fluid?

In lots of vehicles with automatic transmissions, it’s easy to check (and relatively easy to change) your own transmission fluid. It’s just a matter of locating and checking the dipstick for the transmission fluid, not the engine oil. That’s a different dipstick.

Some cars have sealed transmissions and don’t have dipsticks. Check your owner’s manual to see what it says about fluid changes. If your vehicle does have a sealed transmission, that doesn’t mean the fluid cannot or should not be changed. It only makes the process more involved. It might take a professional-level shop, not just what’s in your garage.

One of the great automotive tall tales is the claim that a fluid flush caused the transmission to slip. This phenomenon can happen, but only if the transmission is already worn out. New fluid doesn’t technically cause the slipping. Instead, the old fluid picks up particles from worn-out clutches or gears, which can provide enough friction for the transmission to grab.

That’s all the more reason to change your transmission fluid. Regularly flushing the transmission fluid keeps your transmission in good shape. A fluid flush only makes it perform better.

How to Tell If You Need New Transmission Fluid

A female driver looks concerned. — If it feels like your car is shifting oddly and the transmission fluid is discolored, it’s time for a fluid change.

Even in the best conditions with the best and most attentive driver, transmission fluid eventually goes bad. It doesn’t last forever. Conveniently, symptoms of bad transmission fluid are generally pretty easy to spot.

When you have low or bad transmission fluid, shifting performance decreases, shifting gears gets harder, acceleration suffers, and you might notice your car “hunting” between gears. If the fluid on your transmission dipstick is dark red or black and smells burnt, it needs to be changed.

These symptoms are similar to what happens if you have low transmission fluid. Most cars have a transmission fluid dipstick, which is the easiest way to tell if the fluid is low. To check your transmission fluid, warm the car to operating temperature and let it idle. Pull the dipstick, wipe off the excess oil, and reinsert it. Pull it out again quickly and check the level. The dipstick is marked for low and normal levels. If the fluid is a nice translucent red or pink and is within the hash marks for the correct level, you’re all good.

Replacing Transmission Fluid Is Easy

A mechanic uses an air-powered socket wrench to reinstall an automatic transmission filter. — Always replace the transmission filter and pan gasket when replacing the transmission fluid.

Draining your transmission pan and replacing the fluid, filter, and transmission pan gasket is pretty simple and can be done in about 30 minutes. Check eBay’s video and visual article - opens in new window or tab. for a complete step-by-step guide.

What else should you change when replacing transmission fluid?

If you’re replacing the transmission fluid, you should also replace the transmission filter and the transmission pan gasket. Replacing the filter keeps the fluid clean and healthy for longer, and replacing the pan gasket is a necessary step when replacing the filter.

We recommend replacing the transmission filter every time you change the transmission fluid. An old filter can quickly contaminate the new fluid. Think of changing the filter as relatively cheap insurance. It helps the new fluid last longer.

What should it cost to replace transmission fluid?

Expect to pay $10 to $20 a quart for good-quality transmission fluid. As for the pan gasket and transmission filter, the price depends on the vehicle. For an OEM Toyota filter and gasket you’ll likely pay less than $100, but a BMW or Mercedes part might be a couple hundred bucks.

If you just do a simple transmission fluid change, the job is a straightforward DIY and should be less than $150 with a filter for most cars. For a full flush, expect a shop to charge $200 to $500.

What's the difference between replacing the fluid and a flush?

If you just drain the transmission pan and replace the fluid, you will leave behind a lot of old fluid that stays inside the transmission, even with the engine off.

For a complete flush, you have to pull off transmission lines and run your car so the transmission pumps out all the old fluid. It’s a multi-step process that takes time and patience. Automatic transmissions take a lot of fluid, and a lot of the fluid stays in the torque converter and valve body even when the car is off. The transmission needs to be turning to pump fluid through the system and get it out.

It’s time-consuming, messy, and tricky to get right.

About the author

Aaron Richardson

Aaron learned early on that it's easier to be decent at a bunch of stuff than great at one thing, which led neatly to a career as a writer. He has been an automotive writer, a newspaper editor, and a business reporter, and has always worked on his own cars and bikes. When he isn't writing stories, he's wrenching on a '74 BMW 2002 or riding a motorcycle.

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This article is meant to provide general guidance only. Automotive maintenance, repair, upgrade, and installation may depend on vehicle-specifics such as make and model. Always consult your owner's manual, repair guide for specific information for your particular vehicle and consider a licensed auto-care professional's help as well, particularly for advance repairs.