Transmission Fluid Flush & Change
When your automotive service needs involve your vehicle’s transmission, never forget that most transmission problems start out small but get much worse over time. Taking quick care of any needed transmission repairs can go a long way in saving both time and money. It’s time to get your transmission checked if:
- Your vehicle won’t move
- Difficulty shifting gears
- Transmission seems to be slipping
- Transmission is abnormally loud
- Leaking transmission fluid
- Grinding sounds when shifting gears
- Problems with the clutch
- Check Engine light is on
Frequently Asked Questions
Change transmission fluid every 30,000 miles. Most owner’s manuals say it isn’t necessary. Yeah, right. That’s why transmission shops are making a fortune replacing burned out automatic transmissions. For optimum protection, change the Transmission Fluid and filter every 30,000 miles (unless you have a new vehicle that is filled with Dexron III ATF, which is supposed to be good for 100,000 miles).
The type specified in your owner’s manual or printed on the transmission dipstick.
For older Ford automatics and certain imports, Type “F” is usually required. Most Fords since the 1980s require “Mercon” fluid, which is Ford’s equivalent of Dexron II.
For General Motors, Chrysler and other imports, Dexron II is usually specified.
NOTE: Some newer vehicles with electronically-controlled transmissions require Dexron IIe or Dexron III fluid. GM says its new long-life Dexron III fluid can be substituted for Dexron II in older vehicle applications.
CAUTION: Using the wrong type of fluid can affect the way the transmission shifts and feels. Using Type F fluid in an application that calls for Dexron II may make the transmission shift too harshly. Using Dexron II in a transmission that requires Type F may allow the transmission to slip under heavy load, which can accelerate clutch wear.
It’s a messy job because there’s no drain plug to change the fluid, but you can do it yourself if you’re so inclined. To change the fluid, you have to get under your vehicle and remove the pan from the bottom of the transmission.
When you loosen the pan, fluid will start to dribble out in all directions so you need a fairly large catch pan. You should also know that removing the pan doesn’t drain all of the old fluid out of the transmission. Approximately a third of the old fluid will still be in the torque converter. There’s no drain plug on the converter so you’re really only doing a partial fluid change. Even so, a partial fluid change is better than no fluid change at all.
A typical fluid change will require anywhere from 3 to 6 quarts of ATF depending on the application, a new filter and a pan gasket (or RTV sealer) for the transmission pan. The pan must be thoroughly cleaned prior to reinstallation. This includes wiping all fluid residue from the inside of the pan and scraping all traces of the old gasket from the pan’s sealing surface. Don’t forget to clean the mounting flange on the transmission, too.
When the new filter is installed, be sure it is mounted in the exact same position as the original and that any O-rings or other gaskets have been properly positioned prior to tightening the bolts. Then tighten the bolts to the manufacturer’s recommended specs.
When refilling the transmission with fresh fluid, be careful not to allow any dirt or debris to enter the dipstick tube. Using a long-neck funnel with a built-in screen is recommended.
CAUTION: Do not overfill the transmission. Too much fluid can cause the fluid to foam, which in turn can lead to erratic shifting, oil starvation and transmission damage. Too much fluid may also force ATF to leak past the transmission seals.
Add half a quart at a time until the dipstick shows full. The transmission really isn’t full yet because the dipstick should be checked when the fluid is hot, and the engine is idling with the gear selector in Park. So start the engine, drive the vehicle around the block, then recheck the fluid level while the engine is idling and add fluid as needed until the dipstick reads full.
An auxiliary transmission fluid cooler is easy to install and can substantially lower fluid operating temperatures. The plate/fin type cooler is somewhat more efficient than the tube and fin design, but either can lower fluid temperatures anywhere from 80 to 140 degrees when installed in series with the stock unit. Typical cooling efficiencies run in the 35 to 50% range.