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Automatic Transmission Fluid

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Changing your vehicle's automatic transmission fluid (ATF) isn't as simple as changing its oil, but you can still do it yourself. Be sure to check your vehicle's service manual beforehand, in case your model requires special procedures or needs extra care. Changing the transmission fluid is considered part of regular car maintenance.

Be sure you buy the right transmission fluid and parts even if you have to cough up extra money. Getting the wrong fluid or parts may damage your transmission.

Tools Needed

You'll need a few extra items besides your standard toolbox contents.

  • A transmission filter and gasket plus gasket adhesive.
  • Transmission fluid.
  • A large catch pan.
  • Socket wrenches, screwdrivers and a mallet.
  • Clean cloths and safety glasses.

Cat litter comes in handy to soak up any fluid you spill. To clean the fluid pan, parts cleaner or a similar solvent is useful.

Partial or Full Change?

There are ways to drain and replace all the fluid in your transmission, but the simplest way for beginners is to do a partial replacement. If your vehicle is long overdue for a fluid change and you're new at doing it yourself, you should probably take it to your neighborhood auto mechanic. As you get more experienced at changing ATF, you can teach yourself to pump all the fluid out through the dipstick filler or one of the cooler lines.

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Before you begin changing the fluid, examine it with the dipstick. If it looks good (red) and smells normal (like petroleum), you're okay changing it yourself. If it smells or looks burnt, this could indicate transmission problems, requiring the trained eye of a mechanic. Most manufacturers recommend an automatic transmission fluid change every 25,000 to 30,000 miles.

The method in this article drains almost half of the automatic transmission fluid and replaces it with fresh fluid.

Instructions for Changing Automatic Transmission Fluid

First, locate your vehicle's transmission pan. In some vehicles, you might have to remove sections of the exhaust system. Place a large catch pan under the transmission pan and begin loosening the bolts. Do not remove them all at once, as this will cause a mess. Instead, remove the bolts from all but one side, and then tap the pan to help break the seal. Then slowly remove the remaining bolts in order to slowly tilt the pan away from you and drain into the catch pan.

Measure the old fluid so you know how much to replace. You can do this by pouring it into empty one-gallon milk jugs. Once the bulk of the fluid has drained, remove the other bolts and the pan so you can change the transmission filter. Be careful to keep the pan level, as there will still be plenty of fluid left.

Next, remove the used gasket. Clean any debris from the transmission and transmission pan and its sealing surfaces with parts cleaner or a solvent such as brake cleaner, or a gasket scraper. Make sure to replace the magnet back inside the pan after cleaning, if present, as it is prone to attract metallic parts that would otherwise end up in the transmission and inflict damage.

Remove the old transmission filter. If it is not bolted, the filter will simply pull off with a twisting and pulling motion. If it is of the "pull off" variety, there is usually a new seal that accompanies the filter kit. Be very careful when removing the old seal. If you are worried about damaging or scratching the seal bore, just reuse the old seal.

Finishing Up

Next, install the new filter. Push it into place by hand, or fasten with the attaching screws. If the transmission's original gasket was ridged rubber, and the new one is cork, you should reuse the original gasket, provided it is undamaged as it is considered a reusable gasket and has superior sealing capabilities to cork. If you are replacing a cork gasket with a new cork gasket, then lay the new gasket onto the clean pan making sure that all of the bolt holes line properly and that the gasket is not upside down. Poke the bolts through the bottom of the pan and up through the gasket. The new gasket will hold the bolts in place. Attach the transmission pan to the transmission. If you do not have a torque specification for the pan bolts, just make the bolts "screwdriver tight."

Finally, add the new transmission fluid. Most vehicles allow you to do this through a dipstick tube. Some vehicles require the fluid to be injected through a plugged hole in the transmission while running in park. Start by adding the amount of fluid that has been drained. Then take your vehicle for a short drive and shift through all of the gears.

Last, double check the fluid level. Most vehicles say to check while "hot". This refers to when the dipstick is hot to the touch. Do not overfill the system. You can repeat the flush one or two more times to get all of the fluid replaced with new liquid, but this isn't necessary. As long as you maintain your vehicle's transmission fluid, a partial change every 25,000 to 30,000 miles will suffice.

Remember to seal the used fluid in a container and take it in for recycling. Check with your local recycling center to find out how to properly dispose. Many garages in colder climates will take this from you to fuel waste oil heaters.

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