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 fluid and filter every 30,000 miles (unless you have a new vehicle
that is filled with Dexron III ATF ( Auto Transmission Fluid ) which is supposed to be good for 100,000
miles).

WHY ATF WEARS OUT

An automatic transmission creates a lot of internal heat through friction: the friction of the fluid churning
inside the torque converter, friction created when the clutch plates engage, and the normal friction
created by gears and bearings carrying their loads.

It doesn't take long for the automatic transmission fluid (ATF) to heat up once the vehicle is in motion.
Normal driving will raise fluid temperatures to 175 degrees F., which is the usual temperature range at
which most fluids are designed to operate. If fluid temperatures can be held to 175 degrees F., ATF will
last almost indefinitely – say up to 100,000 miles. But if the fluid temperature goes much higher, the life
of the fluid begins to plummet. The problem is even normal driving can push fluid temperatures well
beyond safe limits. And once that happens, the trouble begins.

At elevated operating temperatures, ATF oxidizes, turns brown and takes on a smell like burnt toast. As
heat destroys the fluid's lubricating qualities and friction characteristics, varnish begins to form on
internal parts (such as the valve body) which interferes with the operation of the transmission. If the
temperature gets above 250 degrees F., rubber seals begin to harden, which leads to leaks and pressure
losses. At higher temperatures the transmission begins to slip, which only aggravates overheating even
more. Eventually the clutches burn out and the transmission calls it quits. The only way to repair the
damage now is with an overhaul -- a job which can easily run upwards of $1500 on a late model
front-wheel drive car or minivan.

As a rule of thumb, every 20 degree increase in operating temperature above 175 degrees F. cuts the life
of the fluid in half!

At 195 degrees F., for instance, fluid life is reduced to 50,000 miles. At 220 degrees, which is commonly
encountered in many transmissions, the fluid is only good for about 25,000 miles. At 240 degrees F., the
fluid won't go much over 10,000 miles. Add another 20 degrees, and life expectancy drops to 5,000
miles. Go to 295 or  300 degrees F., and 1,000 to 1,500 miles is about all you'll get before the
transmission burns up.

If you think this is propaganda put forth by the suppliers of ATF to sell more fluid, think again.
According to the Automatic Transmission Rebuilders Association, 90% of ALL transmission failures are
caused by overheating. And most of these can be blamed on worn out fluid that should have been
replaced.

On most vehicles, the automatic transmission fluid is cooled by a small heat exchanger inside the bottom
or end tank of the radiator. Hot ATF from the transmission circulates through a short loop of pipe and is
thus "cooled." Cooling is a relative term here, however, because the radiator itself may be running at
anywhere from 180 to 220 degrees F.!

Tests have shown that the typical original equipment oil cooler is marginal at best. ATF that enters the
radiator  cooler at 300 degrees F. leaves at 240 to 270 degrees F., which is only a 10 to 20% drop in
temperature, and is nowhere good enough for extended fluid life.

Any number of things can push ATF temperatures beyond the system's ability to maintain safe limits:
towing a  trailer, mountain driving, driving at sustained high speeds during hot weather, stop-and-go
driving in city traffic, "rocking" an automatic transmission from drive to reverse to free a tire from mud
or snow, etc. Problems in the  cooling system itself such as a low coolant level, a defective cooling fan,
fan clutch, thermostat or water pump, an obstructed radiator, etc., will also diminish ATF cooling
efficiency. In some cases, transmission overheating can even lead to engine coolant overheating! That's
why there's a good demand for auxiliary add-on transmission coolers.

AUXILIARY COOLING

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.

ATF FLUID TYPES

What kind of automatic transmission fluid should you use in your transmission? 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.

CHANGING THE FLUID

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.