What is transmission fluid and how do you check it?

Quick insights

• Checking transmission fluid is a different process depending on the type of vehicle and type of transmission.
• Even among the same type of transmission (automatic or manual), the steps you take to check and change transmission fluid could differ.
• When in doubt, check your vehicle’s owner’s manual or visit a qualified professional to check and potentially replace transmission fluid.

Much of car maintenance has to do with taking care of the engine and core components like brakes. Regularly checking the levels of important fluids could also increase a car’s longevity. This is our guide on transmission fluid, including how and when to check it.

What is transmission fluid?

In both automatic and manual transmissions, the fluid is a lubricant that helps the system function. Parts move within your transmission to transmit power from the engine as the gears shift. The lubricant reduces friction and, therefore, heat. Transmission fluid also helps clean and protect components as the system operates.

Is transmission fluid oil?

Transmission fluid and motor oil are not interchangeable. One should not be used in place of the other. Like motor oil, transmission fluid helps lubricate, cool and clean a specific part of your car’s transmission. Plus, similar to oil, there are different types of transmission fluid that can assist or enhance transmission performance and longevity.

How to check transmission fluid

Refer to your owner’s manual or service manual and follow its specific instructions and suggestions about your car’s transmission. The process can vary depending on the type of transmission, and even among vehicles with the same type of transmission.

This is an overview that might help you check the transmission fluid depending on the type of vehicle and transmission you have.

Automatic transmission fluid check

1. Park the car: It’s important to be on a level surface. Set the parking brake and put the car in park. You’ll want the car to remain level and stationary.
2. Warm the engine unless your owner’s manual says otherwise: Start your car and let it run to get the engine (and transmission fluid) to a normal operating temperature. Check the temperature gauge on the dashboard—the needle should be around the midpoint. If your owner’s manual requires you to take a cold reading, skip to step 4.
3. Determine if you should turn the engine off: Consult your owner’s manual for the recommendation. When checking transmission fluid, most automatic cars should be warm. However, the car may have to be running or turned off before you proceed. It depends on the manufacturer.
4. Identify the dipstick: When you open the hood, the dipstick handle may be red, yellow and/or clearly labeled with “ATF” (automatic transmission fluid). If there is a plug instead, you may need to bring your vehicle to a professional to check the transmission fluid.
5. Remove and clean the dipstick: Wipe the dipstick with a clean rag, careful that no lint or debris gets stuck.
6. Reinsert then remove dipstick: Don’t move too quickly. When you remove the dipstick, the fluid may be somewhere between two labels at the bottom of the dipstick.
7. Evaluate the level: The tip of the dipstick may have two sides, one for warm readings and one for cold. You could see a couple pairs of labels: either “Full” and “Add” or “Hot” and “Cold.”
8. Put the dipstick back: You can usually slide the dipstick back in slowly and turn or lock the handle to ensure it’s secure.

Manual transmission fluid check

1. Park on level ground: Set the parking brake to be sure the car doesn’t move.
2. Find the fill plug: Manual transmissions do not usually have a dipstick. Instead, there could be a fill plug on the side of the transmission. Rather than popping the hood, you may need to raise the vehicle with a jack.
3. Remove the plug: You may need a tool to do this, such as a wrench or ratchet.
4. Check the fluid: You can use your finger or a tool that fits into the fill hole. Unless your manufacturer suggests otherwise, a proper level is usually right at the edge of the fill hole.
5. Put the fill plug back: Reinstall the plug securely when you’re finished checking the transmission fluid.

Is an automatic transmission fluid check different?

An automatic transmission check differs from a manual one in several ways:

• Location and procedure: Manual transmissions often have a plug, not a dipstick, to access the transmission. As a result, the exact process of checking, evaluating and replacing the fluid tend to differ.
• Engine temperature: Manual transmissions can usually be checked without running the car, whereas most automatic transmissions should be warm to get an accurate reading.
• Frequency: In general, automatic transmission fluid levels may need to be checked more often than manual ones because of how the system operates.

When to check transmission fluid

Besides times you perform regular maintenance on your car, here are some conditions that might prompt you to check transmission fluid:

• If you experience a transmission issue, such as slipping or rough shifting
• Before and after long trips
• After towing heavy loads, which can stress a vehicle

How often should you check transmission fluid

Manufacturers tend to suggest a frequency for checking transmission fluid in your owner’s manual. The recommended interval could range from every month or once a year. However, stressful driving conditions, including towing and off-roading, might prompt you to check the fluid level afterward. When in doubt, take your car to a qualified professional.

In summary

The process of checking transmission fluid depends on the type of transmission and vehicle you have. In general, warm the engine before checking automatic transmission fluid, and leave the engine cool to check manual transmission fluid.

You’ll have to locate, remove, clean and reinsert the dipstick to get an accurate reading. If there’s a plug instead, make sure the fluid is at the level of the plug. After checking the fluid, reinsert the dipstick or plug before closing the hood.