What Is Transmission Fluid and What Does It Do?

There are many different fluids that run throughout a car. From motor oil to radiator fluid to air conditioning refrigerant, it’s important to keep each of these fluids in check to keep your car in tip-top shape.

Among these essential fluids is transmission fluid. While most people know about the importance of changing their engine oil, many don’t fully understand what transmission fluid is, the role transmission fluid plays and when to change it. However, it’s just as important! 

Keep reading to learn all about transmission fluid, including what it does, the different types, when to change it and more.   

What Does Transmission Fluid Do?

According to AAMCO, UTI’s transmission provider and one of the most trusted and recognized automotive brands in the country, transmission fluid lubricates the bearings and metal parts inside a car’s manual gearbox and keeps them from grinding down as they move.

In an automatic transmission, it not only lubricates the moving parts but also provides hydraulic pressure and friction to make the internal parts work. Transmission fluid in both manual and automatic transmissions also helps to keep the transmission cool. 

Shifting gears is a strenuous task for a car, and transmission fluid is what allows a vehicle to shift with ease without wearing down its parts. While manual transmission oil or fluid has existed in some shape or form since the beginning of automobiles, automatic transmission fluid was created in the 1940s and has played an important role in cars ever since. 

Automatic transmission fluid is not the same as manual transmission fluid. Automatic transmission fluid is a transmission oil that is used in automatic vehicles only but in the case of a manual transmission, where the clutch and shifter are used during gear shifts, manual transmission oil is used.

There are several different types and qualities of transmission fluid, and it’s best to reference your owner’s manual or a trusted auto technician when it comes to choosing the correct fluids for your vehicle.

What Type of Transmission Fluid Do I Need?

In general, there are two main types of transmission fluids: automatic transmission fluid and manual transmission fluid. There is also synthetic transmission fluid, as well as specialty fluids used and specified in various types of transmissions including CVT and dual-clutch models. In order to keep your car running properly, it’s important to know which kind of transmission you have and what specific fluid it requires.

Automatic Transmission Fluid

This type of transmission fluid is designed for cars that have automatic transmissions. It’s also used in some more modern manual transmission cars. Automatic transmission fluid meets the requirements of automatic transmissions and helps with various functions, including:

• Gear lubrication.
• Torque converter operation.
• Valve body operation.
• Clutch friction operation.
• Brake band friction.
• Transmission cooling.

Manual Transmission Fluid

Manual transmission fluid in older vehicles, which is sometimes referred to as manual transmission oil or lube, is common for some older manual transmission cars.

This heavier 75W to 140W fluid is never used in automatic transmission cars, and even if your car is a manual transmission, it doesn’t mean it will use this type of manual transmission fluid.

Most late-model vehicles with manual transmissions will use an automatic fluid in their manual transmissions.   

Synthetic vs. Traditional Transmission Fluid

While traditional transmission fluid is made from crude oil and the reshaping of hydrocarbons for the specifications of different vehicles, synthetic transmission fluid is created through different chemical reactions. This type of transmission oil is less likely to break down, oxidize or thin out in high temperatures.

So how do you choose between traditional and synthetic transmission fluid? Unfortunately, this answer isn’t always black and white. Be sure to check the specifications provided by your vehicle’s manufacturer and when in doubt, consult a transmission specialist.

What Does Transmission Fluid Look Like?

Generally, automatic transmission fluid has a thinner consistency and is clear with a red hue, although some automatic transmission fluids are now blue/green, purple or even amber, depending on the manufacturer. This makes it so that it’s easy to differentiate it from motor oil and the other fluids running through your car. This also makes it easier to spot a leak.

On the other hand, manual transmission fluid is typically a darker color and is thicker in consistency. It will also have a stronger smell.

How Often Should Transmission Fluid Be Changed?

As mentioned previously, many people are aware of the importance of changing motor oil, yet are unaware when it comes to transmission fluid.

Over time, both automatic and manual transmission fluid will break down and become contaminated with particles and debris. While transmission fluid doesn’t need to be changed as frequently as your motor oil, it’s important to keep a close eye on it and check it regularly.

If your transmission fluid level is low or the fluid has started to break down, you’ll notice a decrease in performance when shifting or engaging into gear. This can also increase the risk of damaging internal gears and parts as they begin grinding together due to a lack of lubricant.

Some manufacturers, depending on your style of driving and the type of transmission your car has, recommend changing your transmission fluid every 30,000 to 60,000 miles. However, it’s important to note that this can vary depending on your car’s make and model. Always follow the manufacturer’s recommendations for your specific vehicle.

Towing heavy loads, stop-and-go city driving and harsh weather conditions can cause more strain on your transmission and transmission fluid. If you commonly drive in these conditions, you’ll want to check your transmission fluid levels and condition often to avoid any issues.

How Do I Know if My Transmission Fluid Is Low?

Transmission overheating is the leading cause of transmission failure. Transmission overheating is typically a result of low fluid or depleted fluid due to a lack of regular fluid maintenance. 

If a leak forms in your transmission system, you will lose transmission fluid and eventually be driving with low fluid levels. The transmission will begin to overheat and slip, and while it won’t typically cause the vehicle to stall, it will cause the engine to rev higher than normal or feel as though you have no power.

When your fluid levels are low, this can result in permanent damage to your car’s transmission and lead to costly repairs, rebuilds or even replacements.

Look for signs of leakage on the ground where you park and if your vehicle has a dipstick, check your transmission fluid levels every time you change your oil. If it shows even slightly low, you probably have a small leak that could turn into a larger leak and cause expensive repairs in the future if you don’t address the problem early.

Symptoms of Low Vehicle Transmission Fluid

So how can you tell if your transmission fluid level is low? Here are some key signs to watch out for.

• Puddles: If you ever notice the formation of puddles under your car, it’s likely you have a transmission fluid leak.
• Color: Transmission fluid turning from a light, clear-colored fluid (typically red but in some vehicles, it can be another color) to a darker brown or muddy green color can be a key indicator that it’s time to change your fluid. For reference, check out our transmission fluid color guide.
• Roaring sounds: If you hear roaring when accelerating or going around corners, there may be an issue with your transmission. Additionally, a transmission that is low on fluid may make a whining or buzzing sound.
• Chattering: Another common sign of low transmission fluid is when a vehicle chatters on takeoff. This can feel as though you’re driving over a rumble strip.
• Warning light: Many modern-day cars are equipped with technology to tell you if there is an issue with your transmission. If you ever notice a dashboard light that indicates a high transmission temperature, this means your transmission fluid is hotter than it should be. Keep in mind that your check engine light is not always only about your engine—it can also illuminate if there is a transmission problem.
• Difficulties when shifting: Delays when going into gear or problems when shifting gears, such as slipping, sliding, bumps and noises can be key indicators that there’s an issue with your transmission fluid.
• Transmission slipping or engine revving when going around corners: This is an indicator that you are low on fluid and there is not enough to keep the fluid pick-up in the pan submerged.
• Smell: A slight burning smell, especially if it has an unusual tart smell to it, can be another sign that there’s an issue with your transmission fluid.

If you have any concerns with your transmission fluid, you can easily check its level by pulling the transmission dipstick in most vehicles. Refer to your owner’s manual to learn where to locate the dipstick and the levels your fluid should be at.

In some later-model vehicles, however, there is no dipstick, so it’s best to seek out a professional technician who can put the vehicle up on a lift to check the fluid. 

To learn more about checking your transmission fluid, check out this helpful infographic from AAMCO.

What Happens if a Car Runs Out of Transmission Fluid?

If your car runs out of transmission fluid completely, it will most likely not go into gear, barely move or not shift at all. This is especially the case if you have an automatic transmission car.

Unfortunately, allowing a vehicle to get to the point where it has no transmission fluid will likely lead to extensive and costly repairs. This is why it’s so important to look out for the signs listed above! If you’re ever in doubt, check your transmission or take your vehicle to a professional who can check it for you.

Consequences of Low or Dirty Transmission Fluid

Having low or dirty transmission fluid can lead to a variety of problems that could affect the longevity and performance of a vehicle’s transmission. These include:

• Overheating.
• Transmission slipping or inconsistent shifting.
• Increased wear and tear.
• Loss of hydraulic function.
• Decreased fuel efficiency.

Regular fluid checks and fluid changes are the key to preventing issues within your vehicle’s transmission.

What Is a Transmission Flush?

When it comes to caring for your transmission, you’ll often hear the term ”transmission flush.”

Essentially, a transmission flush helps to ensure there is virtually no old fluid in the transmission, the torque converter or in the vehicle’s oil cooler and cooler lines. It’s a great way to get rid of gunk and grime that can get trapped in your transmission. 

This maintenance process uses a special machine that removes the old, dirty fluid in a transmission and replaces it with new clean fluid, and sometimes a cleaning solution is introduced to enhance the cleaning process.   

Replacing old transmission fluid with fresh fluid and replacing the filter can help prolong the life of your transmission and prevent issues before they happen. AAMCO offers a variety of different fluid change and transmission flush services that you can choose from depending on what your specific needs are. 

Remember, when it comes to caring for your transmission, always refer to the recommendations provided by your manufacturer. The frequency of changing your fluid or having a transmission flush will vary depending on your specific vehicle and the way you use your car or truck.

Learn More From AAMCO, UTI’s Transmission Provider

AAMCO is a transmission repair and total car care franchise. Along with hiring UTI students and graduates, AAMCO provides transmission training aids to select UTI campuses.¹

If you’re looking to learn more about transmission fluid or anything related to caring for your vehicle, check out AAMCO’s blog. Here are a few specific articles related to transmission maintenance:

• AAMCO Automotive Tips
• How to Care for Your Automatic Transmission
• Signs Your Transmission Fluid Filter is Clogged
• 14 Most Common Transmission Problems
• Common Causes and Signs for Slipping Transmission

To learn more about how leading brands like AAMCO work with UTI and support our students, check out our Aftermarket Relationships page. 

Learn Valuable Skills for a Career

Are you passionate about the automotive industry? Want to learn how to maintain and repair transmissions? A career as an automotive technician may be the right fit.

In UTI’s 51-week Automotive Technology program, you’ll be taught everything from automotive engine service and repair to hybrid vehicle system maintenance.⁷ Along the way, you’ll have the support of caring staff and instructors who are committed to the success of our students.

To learn more, visit our website and request information to get in touch with one of our Admissions Representatives today. In the meantime, be sure to check out our FAQs page to find answers to commonly asked questions about UTI’s automotive training.