How To Check and Change Automatic Transmission Fluid

Pouring liquid

Changing your automatic transmission fluid on your own can save you a few dollars. Transmission fluid helps to cool the transmission, and a well-cooled transmission should last 100,000 miles or more. If you decide to change your own, be sure to dispose of the old fluid properly and take precautions to prevent any fluids from contacting your skin or getting into your eyes.

Of course, a mechanic isn't necessary - you can easily change the transmission fluid yourself! Here's how:

  1. Check the fluid level: Let's start out with discussing how to check transmission fluid. Open the hood, start the car and let it idle. Leave the transmission in Park. Always check transmission fluid levels when the car is running. If you try to check the fluid levels when the engine is off, you'll get inaccurate measurements.

    Brush away any dirt, grease or grime that could fall into the dipstick tube. Now remove the transmission fluid dipstick and read the level indicated. New transmission fluid looks red. Old transmission fluid is much darker, almost black.

    Low transmission fluid is always a bad sign. If your transmission fluid is low, it's probably due to a leak either at a gasket or somewhere in the cooling lines that run to the radiator.

  2. Transmission fluid change intervals: Youhow to change transmission fluid may be wondering how often to change your transmission fluid. The recommended interval between changes is usually about 30,000 to 40,000 miles. Many people wait too long to change their automatic transmission fluid, but you should make it part of your basic car maintenance. If you wait until the transmission shifts poorly or begins to slip, then you've probably waited too long and a transmission overhaul might be required.
  3. Drain the transmission fluid: First, set the emergency brake and block the tires to prevent the car from moving. Disconnect a cooling line running from the transmission to the radiator. Connect a piece of rubber tubing to the pipe, and place the free end of the tube into an empty milk jug. Start the engine and let it idle. Transmission fluid should flow out of the cooling line and into the milk jug. As soon as the fluid ceases to flow, turn off the engine. You may have to place the car in Drive in order to get fluid to flow. Be sure to dispose of the fluid properly at a recycling center. Reconnect the cooling line to the radiator.
  4. Remove the drain pan: Remove the bolts holding the drain pan to the bottom of the transmission. This might get a little messy, but it would be worse if you hadn't already removed most of the fluid.
  5. Clean the drain pan: Use some transmission fluid and thoroughly clean the inside of the drain pan. Remove all metal shavings, sludge, and debris. Also clean all of the metal shavings from the magnets on the bottom of the pan.
  6. Replace the filter: Remove the filter and replace with a new one. Don't waste time trying to clean a filter to reuse it; always replace the filter when you change the transmission fluid. Make sure that the O-rings on the new filter are seated properly.
  7. Replace the gasket: It's usually best to replace the gasket sealing the drain pan. You may be able to improve the seal by using black RTV adhesive.
  8. Install the pan: Once the filter and gasket are in place, put the pan back onto the transmission. Hand-thread the bolts for the first few turns so that you won't strip the threading. Use a torque wrench to tighten the bolts to the appropriate tightness.

    DO NOT OVERTIGHTEN the bolts. This can damage the threads in the transmission and dent the pan.

  9. Fill with automatic transmission fluid: Check your owner's manual to determine the correct type and amount of fluid to use in your car. This is usually Dextron III type fluid, but check your owner's manual or a transmission fluid guide just in case your car requires a different type. Check the fluid level using the dipstick with the engine running and the transmission in park. Be careful that you do not add too much fluid.

Changing transmission fluid may seem like a lot of work, but it can save you money if you do it yourself.


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