Ford 1999 Explorer Owner's Manual page 158

Driving
• The 4WD HIGH mode provides
four-wheel drive with full power
to both axles. It is only intended
for severe winter or off-road
conditions, such as deep snow
and ice (where no dry or wet
pavement remains uncovered),
and shallow sand.
• The 4WD LOW mode supplies
four-wheel drive with full power
to both axles and includes a
lower gear ratio for low-speed. It
is only intended for off-road
applications that require extra
power including deep sand, steep
grades and pulling a boat and
trailer out of the water.
The vehicle should not be operated in 4WD HIGH and 4WD LOW
on dry or merely wet pavement. Doing so will produce excessive
noise, increase tire wear and may damage driveline components.
These modes are intended for use only on consistently slippery or
loose surfaces.
If your vehicle is equipped with 4WD or AWD, a spare tire of a
different size than the road tires should never be used. Such a
tire could result in damage to driveline components and make the
vehicle difficult to control.
Utility and four-wheel drive vehicles are not designed for
cornering at speeds as high as passenger cars any more than
low-slung sports cars are designed to perform satisfactorily under
off-road conditions. Avoid sharp turns or abrupt maneuvers in these
vehicles.
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