The next time you check the fluid level in an automatic, sniff the fluid on the end of the dip stick. If it smells like burned toast and/or has a discolored brown appearance, the fluid has cooked itself and is no longer capable of providing proper lubrication to the transmission. If you’re lucky, you may have caught the problem before serious damage has been done — but more often than not by the time the fried fluid is discovered, the transmission is also toast.
Compared to motor oil, ATF has live pretty easy. There’s no soot, gasoline or condensation from combustion blowby to contaminate the fluid. The only physical contaminants the fluid must deal with are particles that wear off the friction plates, gears and bearings inside the transmission. Most transmissions have some type of internal filter to keep the fluid clean. Some do a pretty good job, but others don’t. Most Asian transmissions only have a plastic or metal strainer that can only trap the larger pieces of debris. The rest circulates with the fluid and accelerates wear. Changing the fluid is the only way to get rid of these contaminants.
Heat is the main concern for ATF. Automatic transmissions create a lot of friction, and friction produces heat. The fluid is constantly churning inside the torque converter and being pumped through metering orifices and hydraulic circuits. Every time the transmission shifts gears, the clutch packs generate even more heat that must be carried away by the fluid. The greater the load on the transmission, the more heat it generates and the hotter the fluid gets.
Most ATF can withstand normal operating temperatures of around 200 degrees F for tens of thousands of miles. But if the temperature of the fluid rises above 220 degrees F the fluid starts to break down quickly. Above 300 degrees, fluid life is measured in hundreds, not thousands of miles. And above 400 degrees, the fluid can self-destruct in 20 to 30 minutes!
ATF contains ingredients to improve its oxidation stability as well as other additives to reduce foaming and inhibit corrosion. Over time, the protective additives can also break down causing the fluid’s lubrication properties and viscosity to change for the worse. That’s why fluid breakdown is the leading cause of transmission operating problems and failure. Most experts still recommend changing the fluid and filter every 2 to 3 years or 24,000 to 36,000 miles — or once a year or every 15,000 miles if a vehicle is used for towing or other severe service use.
dipstick fluid level The first thing to check is the fluid level. For an automatic transmission to function normally, the fluid level must be between the “full” and “add” marks on the dipstick. If the fluid level is low, the transmission may slip or engage slowly. If the level is too high, the fluid can become mixed with air (aerated) causing shifting problems, slippage and noise.
Check the level when the transmission is hot. On most vehicles this is done with the engine idling and the transmission in Park. Moving the gear selector thorough each gear position prior to checking the level will help assure an accurate reading.
Under normal driving conditions, a transmission should not use any fluid. A low level, therefore, usually indicates a leak. A visual inspection of the pan gasket and driveshaft seals will tell you where the fluid is going.
Next, check for fluid oxidation. The sniff test is a good one, but a “blotter test’ is even better. Put a few drops of ATF on a clean paper towel. Wait 30 seconds, then examine the spot. If the fluid has spread out and is pink, red or even light brown in color, the fluid is in satisfactory condition. But if the spot hasn’t spread out and is dark brown in color, the ATF is oxidized and should be changed.
If the fluid has a milky brown appearance, it indicates coolant contamination. There is probably a leak in the ATF oil cooler inside the radiator that is allowing coolant to mix with the ATF. This is bad news and needs to be repaired immediately.
If the fluid is full of bubbles or is foamy, the transmission is probably overfilled with ATF. Other causes include using the wrong type of ATF or a plugged transmission vent.
The “old fashioned” way to change ATF is to drop the pan, drain the transmission, replace the filter, reinstall the pan and refill with fresh ATF. Though better than nothing, this approach can leave up to two-thirds of the ATF trapped inside the torque converter (unless the converter has a drain plug, which few do).
A better approach is to use equipment that either attaches to the ATF oil cooler lines or the filler tube to exchange new fluid for old. This approach will replace all of the old fluid. The filter should also be changed to get rid of trapped contaminants, too, because a plugged filter can cause the same kind of problems as a low fluid level or low line pressure.
Always use the type of ATF specified by the vehicle manufacturer. If you don’t know, refer to the owners manual or a reference chart. The type of ATF may also be specified on the transmission dipstick.
Over the years, there have been a confusing array of different ATF types and specifications. Make sure the replacement fluid meets or exceeds all OEM requirements. Using the wrong type of fluid may cause transmission problems and damage.
Type F — Introduced by Ford in 1967 for their automatics. Also used by Toyota.
Type CJ — Special fluid for Ford C6 transmissions. Similar to Dexron II. Must not be used in automatics that require Type F. Can be replaced with Mercon or Mercon V.
Type H — Another limited Ford spec that differs from both Dexron and Type F. Can be replaced with Mercon or Mercon V.
Mercon — Ford fluid introduced in 1987, very similar to Dexron II. Okay for all earlier Fords except those that require Type F. As of July 1, 2007, the production and licensing of Mercon ATF by Ford ends. Ford says applications that require Mercon ATF can now be serviced with Mercon V.
Mercon V — Replaces Mercon. Introduced in 1997 for Ranger, Explorer V6 and Aerostar, and 1998 & up Windstar, Taurus/Sable and Continental. This is the current ATF for most late model Ford products.
Mercon SP — Latest friction-modified ATF for Ford TorqShift Transmissions only. Do NOT use in transmissions that require Mercon or Mercon V.
Dexron — General Motors original ATF for automatics.
Dexron II — Improved GM formula with better viscosity control and additional oxidation inhibitors. Can be used in place of Dexron.
Dexron IIE — GM fluid for electronic transmissions.
Dexron III — Replaces Dexron IIE and adds improved oxidation and corrosion control in GM electronic automatics.
Dexron III (H) — Improved version of Dexron III released in 2003.
Dexron III/Saturn — A special fluid spec for Saturns.
Dexron-VI — Introduced in 2006 for GM Hydra-Matic 6L80 6-speed rear-wheel-drive transmissions. Dexron VI now replaces Dexron III and II, and can be used in GM or import transmissions that formerly specified Dexron III or II.
Chrysler 7176 — For Chrysler FWD transaxles.
Chrysler 7176D (ATF+2) — Adds improved cold temperature flow and oxidation resistance. Introduced 1997.
Chrysler 7176E (ATF+3) — Adds improved shear stability and uses a higher quality base oil. Required for four-speed automatics (do NOT use Dexron or Mercon as a substitute).
Chrysler ATF+4 (ATE) — Introduced in 1998, ATF+4 is synthetic and replaces the previous ATF+3 fluid. Used primarily for 2000 and 2001 vehicles, it can also be used in earlier Chrysler transmissions (except 1999 and older minivans with 41TE/AE transmission). ATF+3 should continue to be used for 1999 and earlier minivans because of the potential for torque converter shudder during break in.
NOTE: Chrysler ATF+4 Must always be used in vehicles that were originally filled with ATF+4. The red dye used in ATF+4 is not permanent. As the fluid ages it may become darker or appear brown in color. ATF+4 also has a unique odor that may change with age. Therefore, do not relay on the color and odor of ATF+4 to determine if the fluid needs to be changed. Follow the OEM recommended service interval.
Chrysler ATF+5 for 2002 and newer models.
BMW LT7114l or LA2634 — Special formula for BMW transmissions.
Genuine Honda ZL ATF — Special ATF for Honda automatics (except CVT applications).
Mitsubishi Diamond SP-II & SP-Ill — Special formula ATFs for Mitsubishi transmissions, also Hyundai and Kia.
Nissan HP/J-Matic — Special formula for Nissan, Infiniti and some Subaru transmissions.
Toyota Type T, T-III & T-IV — Special formula ATFs for Toyota, Lexus and Scion transmissions.
NOTE: There are a number of aftermarket synthetic ATF fluids that claim to meet numerous OEM requirements. Refer to the product label for approved applications. Make sure the product meets the specific requirements for your vehicle application before using it as transmission shift problems and possible damage may result from using the wrong type of ATF!