What is this?
 Transmission fluid is a slippery liquid that
 acts as a lubricant for all of the moving
 parts inside your transmission. In an
 automatic transmission, this fluid also
 serves as a “coolant” and a viscous fluid
 that transmits power from the engine to
 the transmission.

 A variety of fluids are used for different
 transmissions. Automatic transmissions
 use something called — shockingly —
 automatic transmission fluid (ATF).
 Manual transmissions use a variety of
 oils: regular motor oil, heavyweight
 hypoid gear oil or even automatic
 transmission fluid in some cases. Your
 owner’s manual will tell you what your
 transmission calls for.

 Should I do this service when it’s
 recommended?
 Yes, definitely, regardless of whether you
 have a manual or an automatic
 transmission.

 Manual: Most manufacturers
 recommend that manual transmission
 fluid be changed every 30,000 to 60,000
 miles. Under heavy-duty use, some
 manufacturers suggest changing
 transmission fluid every 15,000 miles.

 Automatic: Service intervals for an
 automatic transmission vary from every
 30,000 miles . . . to never. The typical
 service interval is 60,000 to 100,000
 miles. Changing it more often does no
 harm.

 Why do I have to do this?
 Manual: In a manual transmission, the
 problem is not so much the fluid
 degradation, but rather fluid
 contamination. This contamination
 occurs over time as the synchronizers,
 bearings and gears in the transmission
 wear out. The resulting metal particles
 then float around in the lubricant. And we
 all know that oil with microscopic
 particles of metal in it does not lubricate
 as well as clean oil. So if these
 contaminants are not drained out, they
 will shorten the life of your transmission.

 Automatic: Because more heat is
 generated in an automatic transmission,
 automatic transmission fluid actually
 degrades and breaks down with use.

 In addition, like in a manual transmission,
 automatic transmission fluid will also
 become contaminated with worn bits of
 the transmission. If these contaminants
 are not drained out, they will shorten the
 life of your transmission.

 What happens if I don’t do this?
 If you don’t change the transmission fluid
 on schedule, you’ll be lubricating your
 transmission with metal shavings and
 other contaminants. This will shorten the
 transmission’s life. The result could be a
 hefty boat payment to your mechanic. In
 other words, changing your transmission
 fluid at the correct interval is a good
 investment.

 Can I do this myself?
 Whether you have a manual or an
 automatic transmission, we don’t
 recommend that you do this service
 yourself. Changing the transmission fluid
 is a disgusting, messy job. It’ll cost you a
 perfectly good set of clothes, in addition
 to the fluid itself. Besides, it’s not
 particularly expensive to have it done at a
 garage.

 Lots of shops now have a special
 transmission flushing machine that can
 replace all of the fluid in a transmission,
 as well as a separate lock-up torque
 converter, which removes fluid that you
 won’t be able to get at if you just drain
 the system using “gravity” at home.

 Finally, if you decide to change your
 transmission fluid at home, you’ll need to
 properly dispose of your old
 transmission oil when you’re done,
 which may be difficult — unless you pour
 it into your neighbor’s flower beds at
 night.

 Is there any maintenance required
 between intervals?
 Yes. It’s important to regularly check the
 transmission fluid level between service
 intervals. Letting your car run low on
 transmission fluid can cause the
 transmission to shift improperly — or not
 at all. It also can harm the internal parts
 of your transmission, which will not be
 properly lubricated. Unfortunately, you
 may not hear any noises or have other
 clues that your transmission is low on
 fluid, until it’s too late. So it’s important to
 get it checked.

 Here’s how you can check your
 transmission fluid level:

 Manual: Checking the transmission fluid
 in a manual transmission can be difficult.
 A few thoughtful manufacturers have
 included a dipstick, but that’s the
 exception rather than the rule. If you own
 a car with a manual transmission, we
 suggest that you ask your mechanic to
 check the fluid level when your car is up
 on the lift during an oil change. It takes
 just a minute.

 Automatic: If you own a car with an
 automatic transmission, your car will
 have a dipstick for this purpose. Be
 careful not to make the common mistake
 of confusing the transmission dipstick
 with the crankcase dipstick.

 For most cars, checking the automatic
 transmission fluid consists of pulling the
 transmission dipstick out while the
 engine is warmed up and running and
 with the transmission in park. We
 suggest that you check your owner’s
 manual, however, since some
 manufacturers may have a different
 procedure.

 Of course, always check your fluid level
 if you notice a leak of any kind.

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