Lincoln 2002 Continental Owner's Manual page 142

Driving
D (Overdrive)
The overdrive position is the normal
driving position for an automatic
overdrive transaxle. It works the
same way as 3 (Third) but shifts to
a fourth gear — an overdrive gear
— when your vehicle cruises at a
constant speed for any length of
time. This fourth gear will increase
your fuel economy when you travel
at cruising speeds.
Overdrive may not be appropriate for certain terrains. If the transaxle
shifts back and forth between third and fourth gears while you are
driving hilly roads or if your vehicle requires additional power for
climbing hills, shift into 3 (Third).
When to use 3 (Third)
3 (Third) eliminates the needless
shifting back and forth between
third and fourth gears that your
vehicle may do when driving on hilly
terrain. It also gives more engine
braking than overdrive to slow your
vehicle on downgrades.
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