According to the Automatic Transmission Rebuilders Association (ATRA), fluid breakdown is still the number one cause of most transmission failures. Worn-out, oxidized transmission fluid can't provide the same level of lubrication and protection as fresh fluid. Contaminants in the fluid and varnish buildup on critical surfaces take a toll over time. Dirty worn-out fluid can cause control valves to stick, and bearings and clutches to fail inside the transmission.
The friction modifiers in ATF play a critical role in the operation and longevity of late-model electronic automatic transmissions. Friction modifiers are chemical additives in the fluid that affect how the transmission feels when it shifts gears. Vehicle manufacturers have specifications for the type and amount of friction modifiers that are required for their transmissions. The specifications differ from one make and model of vehicle to another depending on which transmission they have and the mechanical differences in the torque converters and clutch packs. That's why Ford, Chrysler, General Motors, Honda, Toyota, Nissan and the other OEMs have so many different ATF formulations.
As the miles add up, heat and constant shearing break down the ATF. The friction modifiers are one of the first things that go, and once that happens, shifts may become rough and jerky - a condition known as transmission shudder.
Driving conditions that increase the normal operating temperature of the fluid accelerate oxidation. This includes things like aggressive driving, pulling a trailer, mountain driving, highway driving with increased wind resistance due to a car-top carrier, high speed driving during unusually hot weather, etc.
Most ATF can handle normal operating temperatures of 175 to 190 degrees F. But as the operating temperature goes up, the life of the fluid drops. For every 20 degree increase in fluid temperature beyond the normal range, the life of the fluid is cut roughly in half! That's why many vehicle manufacturers recommend changing the ATF at 15,000 miles if a vehicle is subjected to "severe use" instead of the usual 30,000 mile interval for normal use.
Worn-out transmission fluid usually has a burnt smell and a discolored brownish appearance. A "blotter test" can also be used to reveal the fluid's condition. Place one or two drops of ATF from the transmission on a paper towel and wait about half a minute. If the spot is widely dispersed and red or light brown in color, the fluid is still good. But if the spot does not spread out and is dark in color, the ATF is oxidized and should be changed.
Change Transmission Fluid
Some fluid exchange/flush machines also allow the use of a cleaner product to remove varnish and sludge from neglected transmissions. If the machine has a pressure gauge, you can use it to detect possible restrictions in the transmission fluid circuit (filter, lines or ATF cooler). Normal pressure readings may be as low as 8 to 10 psi with some vehicles. Readings less than 8 psi may indicate a restriction.
Always use ATF that meets the vehicle manufacturer's requirements. Refer to the owners manual or dipstick for the type of fluid required. Using the wrong type of fluid may cause shift problems and possible transmission damage!
For more information about ATF, see: Automatic Transmission Fluid (types and applications)|
Automatics with No Dipsticks According to the automobile manufacturers research, a certain percentage of automatic transmission failures are caused by over-filling and/or using the incorrect transmission fluid. It is important to remember to NEVER over-fill the transmission assembly and to ALWAYS use the recommended transmission fluid. To discourage over-filling, some vehicle manufacturers have eliminated the dipstick on the transmission. Unfortunately, this also makes it hard to tell if the fluid level is low. On automatic transmissions that do not have a dipstick to check the fluid level or add fluid, a fill plug is usually located on the left side or right side of the transmission. On some, there may also be a drain plug on the bottom of the transmission. To check the fluid level, the transmission must be warm and the vehicle must be parked on a level surface or raised on a lift. Jacking up the front wheels will tilt the vehicle and give an innaccurate indication of the fluid level. Therefore, all FOUR wheels must be raised off the ground and the vehicle must be properly supported by four jack stands. NEVER crawl under a vehicle unless it is safely supported by jack stands. When the fill plug is removed, some fluid should dribble out of the hole if the fluid is at the proper level (flush with the bottom of the fill plug hole). If no fluid comes out, add fluid to bring it up to the level of the hole. Below are some of the automatic transmissions that do not have a dipstick: 5-SPEED 2004-UP ACURA TL, RL, RSX 5L40/5L50E 2004-05 CADILLAC CATERA AISIN 81-40LE 2004-05 CHEVROLET AVEO 4T40/45E 1997-UP CHEVROLET CAVALIER, COBALT 42RLE 2005-UP CHRYSLER 300 3.5L 2WD NAG-1 2005-UP CHRYSLER 300 3.5L AWD AF33 2005-UP CHEVROLET EQUINOX 5R55N/S/W 2005-UP FORD CARS AISIN RNJ 1998-05 ISUZU NPR DIESEL ZF-6SHP-26 2005-UP LINCOLN NAVIGATOR 5.4L 5F31J 2004 MAZDA MPV W/5SPD N4AEL 2004 MAZDA MIATA AF23 2004-05 SATURN ION 4/5-Speed 2004-05 SATURN VUE |
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