Transmission fluid serves to cool, lubricate, and provide a barrier between the moving parts of your car’s transmission. In an automatic transmission, the fluid is also used to create hydraulic pressure, which acts on a collection of clutches (and sometimes bands) to operate the planetary gear sets that allow your car to shift.
Furthermore, automatic transmission fluid (ATF) is fundamental to the operation of the torque converter—a device that creates torque multiplication and acts as a type of clutch between the engine and transmission.
How to Check Transmission Fluid (in Cars With Automatic Transmission)
Transmission fluid is designed to work at high temperatures. But over time, the fluid will start to break down—which is why you should check it regularly and perform a transmission fluid change on the date/schedule and mileage recommended by the vehicle manufacturer.
You can find the transmission fluid service schedule in your owner’s manual.
The procedure below details a step-by-step guide on how to check transmission fluid in cars that have a dipstick for the ATF.
1. Park your car on a flat and level surface.
2. Set your transmission to Park and start your engine.
3. Set the parking brake and step on the brake pedal. Starting from Park, move the gear selector through the entire gear range, then go back to Park again.
4. Locate your transmission fluid dipstick. It should be under the hood and marked or colored appropriately. Take out the dipstick and wipe it off with a clean rag.
5. Reinsert the dipstick, then remove it again to check the fluid level. If your vehicle has been sitting and the engine is cold, the transmission fluid level should be at the full “cold” mark.
6. Let your transmission reach operating temperature. This step is important because ATF expands in high temperatures.
7. Insert the dipstick and remove it again so you can check the fluid level.
8. Some dipsticks have “hot” and “cold” level marks engraved on them while others simply feature a crosshatch pattern. Your transmission fluid should be at the “hot” level or within the crosshatch pattern. This means that your transmission fluid is at the right level.
Note: It’s important to note the condition of the ATF as you’re checking the level. Most vehicles use red or pink ATF. Transmission fluid that’s turned light brown means that it’s overdue for service. However, if the fluid looks black and/or smells burnt, it means that there’s a problem with your transmission.
Keep in mind that, nowadays, most cars do not have a transmission dipstick. In many modern cars, you’ll need to check the transmission fluid level from underneath the vehicle. What’s more, some newer cars require a scan tool to check the transmission fluid level. And some vehicles have their transmissions sealed, so there’s no way to check or service the fluid.
For these reasons, it’s important to check your owner’s manual before attempting to check or service your transmission fluid.
Also, even if your car has a dipstick, it’s a good idea to consult the owner’s manual before checking the ATF, as there are often discrepancies in the fluid-checking process. The steps we’ve listed above are only a general guide.
How to Change Transmission Fluid (in Cars With Automatic Transmissions)
As was mentioned earlier, these days you’ll find that there are different types of automatic transmission designs. So before attempting to service your transmission, you should consult a repair manual to determine the correct procedure.
The following generic outline is for a transmission that has both a dipstick and a removable pan.
Also, you should only need the most basic shop tools to change your automatic transmission fluid. These tools include:
- Correct automatic transmission fluid
- New transmission filter and gasket (AKA transmission filter kit)
- Jack and jack stands
- Socket set and ratchet
- Longneck funnel
- Clean rags
- A two-gallon container or catch pan
- Tarps, cardboards, or newspapers
- Torque wrench
Once you have gathered all the necessary tools, you can move forward with changing your transmission fluid. Here’s how it’s done:
1. Make sure that the vehicle has been sitting long enough that the engine and transmission are cool. Hot transmission fluid can cause severe personal injury.
2. Safely raise and support the vehicle using a jack and jack stands. Set the parking brake and chock the rear wheels.
3. Set the two-gallon container or catch pan on a piece of tarp or some newspapers and position it under the transmission pan.
Loosen the bolts of the transmission pan to allow the fluid to drain. Then, remove all but a few of the pan bolts. Angle the end of the pan that has all of the bolts removed downward and dump all remaining fluid into the container. Then, unscrew the rest of the bolts and remove the transmission pan.
4. Remove the old gasket. Next, clean the mounting area on the transmission with the solvent to remove any remaining debris.
5. Remove and replace the transmission filter and seal properly.
6. Clean the bottom of the transmission pan with the solvent and a lint-free rag (or allow it to air-dry).
7. After everything is clean, you can install the new gasket and the transmission pan. Start by placing the gasket on top of the pan. Then, insert a couple of bolts through the pan to hold the gasket in place. Thread those bolts into the transmission by hand.
8. Once the pan is in place, you can thread the rest of the bolts in (also by hand). Next, use a torque wrench to tighten the bolts to the manufacturer’s specification.
9. Carefully remove the jack stands and lower the vehicle.
10. You can now open the hood. Pull out the transmission fluid dipstick, insert your funnel, and slowly pour in the new transmission fluid. Make sure to fill it to the proper level—do not overfill the transmission.
11. Take the funnel out and replace the transmission fluid dipstick. Repeat the steps outlined in the “How to Check Transmission Fluid” section to ensure the fluid is at the proper level.
Note: Always use the appropriate transmission fluid specified by your car manufacturer. If in doubt, consult your owner’s manual or ask your local dealership parts department.
How Often Should You Change Your Transmission Fluid?
Typically, automatic transmission fluid lasts between 60,000 and 100,000 miles. But to find out the correct service interval for your car, make sure to check the maintenance schedule outlined in the owner’s manual.
The service interval may be shorter for some vehicles and longer for others. Some vehicles may not even require the transmission fluid to be changed because the transmission is sealed.
How Does Transmission Fluid Deteriorate?
Most transmission fluids simply break down over time. There are, however, certain conditions that can cause ATF to deteriorate more quickly than usual.
For example, hauling heavy loads, trailer towing, and frequent stop-and-go driving can cause the transmission to run hot, thereby causing the fluid to degrade quickly. Transmission problems can also cause the fluid to overheat and break down.