Considering the fact that it costs $1,500 to $3,000 or more to
replace a transmission or transaxle these days, the cost of a fluid
and filter change is peanuts by comparison.
$30 to $60 every 30,000 miles to have the ATF replaced can be one of
the smartest investments a motorist can make. Just like regular oil
and filter changes, replacing the ATF for preventive maintenance can
reduce the risk of a premature transmission failure and the need for
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.
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.
Always use ATF that meets the vehicle manufacturer's requirements.
Refer to the owner's manual or dipstick for the type of fluid
required. Using the wrong type of fluid may cause shift problems and
possible transmission damage.