How to Check and Add Fluid to an Automatic Transmission

Park the car on a level surface with the engine running. You might want to cycle through each gear quickly before parking the car.

Lift the hood. Cars typically have a lever inside, next to the driver’s side, to raise the hood. Refer to the owner’s manual if you can’t find it.

Locate the automatic transmission fluid line. On many newer vehicles, the transmission fluid line is labeled, but if not, refer to the owner’s manual to find its location.

• For rear-wheel drive vehicles, the dipstick is located at the back of the engine, above the oil reservoir.
• For front-wheel drive vehicles, the dipstick is usually at the front of the engine, connected to the transmission. On most cars, it will be on the right side of the oil reservoir.

Remove the transmission dipstick. Wipe it with a clean rag or paper towel, reinsert it and remove it again to check the transmission fluid level. The fluid should be between the “Full” and “Add” marks or between the “High” and “Low” lines.

• Typically, you won’t need to add transmission fluid. However, if the level drops significantly below the “Add” mark or the “Low” line, your system may be leaking and you should have the car repaired.

Check the condition of the transmission fluid. Good automatic transmission fluid is usually red (although sometimes it can be pink or light brown) and should not have bubbles or a burnt smell. If any of the following occur, take your car for repairs.

• If the transmission fluid is brown or smells like burnt toast, it means the fluid has overheated and can no longer properly dissipate the heat from the transmission. You can further inspect the fluid by placing a few clean sheets of paper and waiting about 30 seconds to see if the fluid spreads. If not, you need to change the fluid immediately, or the transmission itself may be severely damaged.
• If the transmission fluid is milky brown, it’s been contaminated by coolant leaking from the radiator and entering the transmission cooler. Take your car for repairs immediately.
• If the transmission fluid is foamy or bubbly, it means there’s too much fluid in the cylinder, or you may be using the wrong type of fluid or there could be a blockage in the transmission vent hole.

Add transmission fluid if necessary. Add a small amount of fluid each time, checking the level regularly until it reaches the proper level.

• When you first drive the car, you may need to add to 4.5 liters of transmission fluid if you’ve replaced the entire vehicle engine and started fresh. Otherwise, check the dipstick frequently to avoid overfilling the fluid reservoir.

Start the car and, if possible, cycle through the gears. This process helps circulate the new fluid and lubricate each gear. Begin with the car parked and the engine running. If possible, lift the wheels off the ground. Go through gears One to Three, including Drive, Overdrive, and Reverse, stopping in each gear for about a minute to ensure the fluid is distributed evenly. When finished, let the engine run for a few more minutes before driving the car to the parking lot.

Check the dipstick again to determine how much more fluid you need to add. Examine the dipstick, as transmission fluid can splash from the reservoir to other gears, indicating the need for additional fluid.

Add the necessary amount of fluid to reach the standard level. Depending on whether you are just topping up the fluid or replacing the entire fluid reservoir, you may need to add more fluid at this stage.

• If you're simply topping up, you'll only need to add around 1 liter or less.
• If you're replacing the entire fluid reservoir and starting fresh, you may need to add between 4.5 to 1 liters, depending on the manufacturer and model of your car.

Complete the process. Your transmission fluid is now at the correct level, and your car should run smoothly.