Ford F-150 Owner's Manual page 544

Exceptions
There are several exceptions to the Normal
Schedule.
Axle and Transfer Case Maintenance
Axle(s) and transfer case (4X4 only) fluid
changes or level checks are not required
unless a leak is suspected or the assembly
has been submerged in water. During long
periods of trailer towing with outside
temperatures above 70°F (21°C) or at
wide-open throttle for long periods above
45 mph (72 km/h), change the rear axle
fluid every 30,000 mi (48,000 km), if the
rear axle is filled with non-synthetic fluid.
This interval can be waived and the
150,000 mi (240,000km) service interval
can continue if the rear axle is filled with
75W85 synthetic gear fluid meeting Ford
specification WSS-M2C942-A, part
number XY-75W85-QL, or equivalent. Add
friction modifier XL-3 (EST-M2C118-A) or
equivalent for complete refill of
Traction-Lok rear axles.
F-150 (TFC) Canada/United States of America, enUSA, Edition date: 201607, Second Printing
Scheduled Maintenance
541
California Fuel Filter Replacement
If you register your vehicle in California, the
California Air Resources Board has
determined that the failure to perform this
maintenance item does not nullify the
emission warranty or limit recall liability
before the completion of your vehicle's
useful life. Ford Motor Company, however,
urges you to have all recommended
maintenance services performed at the
specified intervals and to record all vehicle
service.
Hot Climate Oil Change Intervals
Vehicles operating in the Middle East,
North Africa, Sub-Saharan Africa or
locations with similar climates using an
American Petroleum Institute (API)
Certified for Gasoline Engines (Certification
mark) oil of SM or SN quality, the normal
oil change interval is 3,000 mi (4,800 km).
If the available API SM or SN oils are not
available, then the oil change interval is
1,800 mi (2,900 km).
Engine Air Filter Replacement
The life of the engine air filter is dependent
on exposure to dusty and dirty conditions.
Vehicles operated in these conditions
require frequent inspection and
replacement of the engine air filter.