How to Change Transmission Fluid (2024)

Understanding the Importance of Transmission Fluid

Your transmission needs clean fluid – and the right amount – to stay healthy. Typically starting out as a pinkish or reddish translucent fluid, it’s much more than a crude oil product. Here’s what roles it performs:

• Lubrication – Transmission fluid provides lubrication to the various moving parts within the transmission system. This helps reduce friction and wear on components like gears, bearings, and shafts.
• Heat dissipation – The transmission generates a significant amount of heat during operation. Transmission fluid helps dissipate this heat, preventing overheating of the transmission components. Overheating can lead to damage to the clutches, other hard parts, and the fluid.
• Cooling – In addition to dissipating heat, transmission fluid also helps in cooling the transmission system. Many vehicles have a transmission cooler, and the fluid circulates through it to maintain an optimal operating temperature.
• Seal function – Transmission fluid helps in maintaining proper seals that prevent fluid leaks and maintain the necessary pressure levels for the transmission to operate effectively. If the fluid level is low or the fluid is old and degraded, it can lead to seal failure and leaks.
• Friction modification – Transmission fluid contains additives that modify friction characteristics. These additives help optimize the friction between the transmission clutches and bands, ensuring smooth and precise shifting.
• Cleaning and protection – Transmission fluid acts as a cleaning agent, helping to remove contaminants and debris from the transmission components. It also provides a protective film on metal surfaces, preventing corrosion.

When to Change Your Transmission Fluid: Signs and Milestones

When to change your transmission fluid comes at the behest of a few factors. Some factors include the climate, towing, offroading, and other concerns that can affect the fluid’s longevity. How often to change transmission fluid will vary according to the vehicle and its frequency of use.

Many manufacturers in the 1990s and early 2000s began developing synthetic and specific-type transmission fluids, and with this, extended the service life of the fluid, sometimes even declaring a “lifetime fluid”.  In retrospect, this led to many transmission failures due to the continued neglect of the fluid. As transmission fluid begins to degrade, the temperature inside the transmission will get higher during operation, leading to further breakdown of the fluid, which leads to failures such as clutch pack slippage, banging or knocking going into gear, pump failure, and ultimately, transmission failure.

Check your vehicle’s owner’s manual for the recommended change frequency, and also ask for recommendations within your community of ownership on car forums and the internet. Many vehicles over time become very failure-prone to transmission issues that the original manufacturer was not aware of at the time of recommendation, and changing the fluid more often will help keep the transmission operating properly.

Key Indicators for Transmission Fluid Change

Not sure when to change the fluid in your transmission? Here are the signs to watch for:

• A service indicator going off. Some vehicles have a maintenance indicator that specifies it’s time to change the transmission fluid.
• A Check Engine Light on with transmission-related codes. DTCs like ‘transmission loss of prime’ can indicate fluid issues, and a fluid flush is the first line of defense.
• Deteriorated fluid condition. Fluid that’s dark brown or black is long past due for a change, or if there are metal flecks or moisture in the fluid.
• You’ve reached the service interval. If you reach the time or mileage to change the fluid, don’t put it off.
• Burnt fluid. If the transmission fluid odor is burnt-smelling and takes your breath away, it needs an immediate service.

Recommended Mileage Intervals for Different Vehicles

A common, one-size-fits-all recommendation for when to change your transmission fluid is every 30,000 to 60,000 miles, or five years, based on normal, everyday driving. Truck owners who do frequent towing, or constant stop-start city drivers need to move this interval into the 20 to 25,000-mile range. Like engine oil, changing transmission fluid too much will never hurt anything but your wallet.

DIY Guide: Step-by-Step Transmission Fluid Change

Different vehicle designs will have processes that depart from these steps. However, the following is a general guide on how to change the transmission fluid.

Step 1: Lift your vehicle

Use a jack or ramps and raise the vehicle according to the manufacturer’s recommended lift points, or drive onto the ramps. Set your parking brake.

Step 2: Find the transmission pan and set up

Locate the transmission’s oil pan and place a drain pan to catch the old transmission fluid.

Step 3: Drain fluid

Some transmission pans will have a drain bolt, which saves a lot of trouble. Others, you will need to loosen the pan bolts that will begin draining the old transmission fluid, and eventually, the pouring of the fluid out around the edge of the pan. Beware, the old fluid may be hot, and the more you loosen the bolts, the faster it begins to flow.

Step 4: Inspect the transmission pan

Take the transmission pan and inspect carefully. Many pans will have a provision with a magnet stuck to it on the inside, to gather small metal particles in the fluid. Don’t be alarmed by metallic “gunk” on the magnet. This is very normal from general wear, but large metallic chunks are not normal. Clean the pan with degreaser or in a parts washer, and wipe dry.

Step 5: Replace the pan gasket

Replace the transmission pan gasket and filter being sure to carefully follow the filter replacement and proper gasket placement. Many use RTV sealant instead of a gasket, and you need to ensure that both sealing surfaces are spotless for it to seal properly.

Step 6: Re-install the pan and secure the bolts

After installing the pan, tighten the pan bolts to the recommended torque.

Step 7: Add fluid

Fill your transmission through the dipstick hole with a funnel and leave about a ½ quart of fluid in your last bottle. Some transmissions will have a separate fill hole, but this is rare. Some vehicles, like Land Rovers, do not have a dipstick or fill hole up top, and a fluid extractor must be used to fill. Again, the owner’s manual and online will give you the best advice here.

Step 8: Start the vehicle and shift

You’ll now start the vehicle, and take the vehicle into drive, then up to reverse, and back to park, waiting about two seconds in each spot. Repeat this process a few times.

Step 9: Check the fluid level

Now, remove the dipstick and check the fluid level. Add the additional ½ quart of fluid if needed. Once your fluid is at the desired level, repeat step 8 one additional time, to make sure that fluid has circulated through all the circuits properly, and re-check.

Step 10: Check your work

Lastly, with the vehicle running, check underneath for any drips or leaks. Test drive the vehicle.

Choosing the Right Transmission Fluid: Types and Recommendations

Transmissions today are much different than the transmissions of 40 years ago. Back then, there were only 2 types of Fluid used – Dextron/Mercon, or Ford Type F. Today, there are over 15 different variants of transmission fluids, and many manufacturers insist using on their specific fluid for the transmission. While all manufacturers will typically always recommend “their” fluid for the transmission, there are indeed many cases where the original fluid is the only option. Because of this, it is vitally important that you not only research your owner’s manual, but also check carefully online to determine what your vehicle’s transmission takes, and if there are indeed alternatives that work as well or better.

AutoZone carries transmission fluid options of virtually every type. Along with vehicle-specific fluids, you’ll find multi-vehicle ATF options for both automatic transmissions and CVTs. What’s most important is that the fluid you choose contains certifications for your vehicle, so carefully check the label before adding a fluid to your transmission.

Common Mistakes to Avoid During Transmission Fluid Change

When you’re changing your transmission fluid, there are a few pitfalls to watch out for. One of the most common is not making sure that the fluid level is proper after the service. Always double-check that the level is correct at the end, and check the fluid every oil change service and add fluid as required.

Also, it might be tempting to not take the fluid requirements seriously. But engine oil, transmission fluid, gear oil, and power steering fluid are all very different in composition, never mind the less distinct nuances between tranny fluid variations. The wrong spec can cause transmission fluid symptoms immediately, and sometimes with lasting effects.

Always use the correct type of transmission fluid, following the manufacturer’s guidelines. That’s how you’ll get the best life out of your vehicle.

Shop AutoZone for your transmission fluid and any other lubricants and parts you need to take care of your vehicle. All the top brands, along with expert advice, are found in one place.

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