Ford Explorer 1998 Owner's Manual page 172

Maintenance and care
An overfill condition of transmission fluid may cause shift and/or
engagement concerns and/or possible damage.
Do not drive the vehicle if the fluid
level is below the bottom hole on
the dipstick and outside
temperatures are above 10°C (50°F)
(see figure to the right).
Your transmission does not use up fluid. However, it is recommended
that you check the transmission fluid at least twice a year. The fluid level
should be checked if the transmission is not working properly, i.e., if the
transmission slips or shifts slowly or if you notice some sign of fluid
leakage.
Transmission fluid should be checked at normal operating temperatures
66°C-77°C (150°F-170°F) on a level surface. The normal operating
temperature can be reached after approximately 32 km (20 miles) of
driving.
The transmission fluid should be in
this range if at normal operating
temperature (66°C-77°C
[150°F-170°F]) (see figure to the
right).
The transmission fluid should be in
this range if at room temperature
(10°C-35°C [50°F-95°F]) (see figure
to the right).
If your vehicle has been operated for an extended period at high speeds,
in city traffic during hot weather or pulling a trailer, the vehicle should
be turned off for about 30 minutes to allow the fluid to cool before
checking.
1. Park the vehicle on a level surface and engage the parking brake.
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