Ford Super Duty Owner's Manual page 408

Scheduled Maintenance
Extensive Idling or Low-speed Driving for Long Distances as in
Heavy Commercial Use (i.e., Delivery, Taxi, Patrol Car or Livery)
Every 5000 miles Change engine oil and filter.
(8000 km) or six
Inspect and lubricate U-joints.
months
Every 30000 miles Replace front wheel bearing grease and grease
(48000 km) seals if non-sealed bearings are used.
Every 60000 miles Change transfer case fluid (4WD vehicles).
(96000 km)
Replace spark plugs.
*
Vehicles equipped with dual rear wheels should rotate the front wheels
when specified; rear wheels only if unusual wear is noted.
Operating in Dusty or Sandy Conditions Such as Unpaved or
Inspect frequently, Replace engine air filter.
service as required
Every 5000 miles Inspect the wheels and related components for
(8000 km) abnormal noise, wear, looseness or drag.
Rotate tires
tread depth.
Every 5000 miles Change engine oil and filter.
(8000 km) or six
Inspect and lubricate U-joints.
months
Every 30000 miles Replace front wheel bearing grease and grease
(48000 km) seals if non-sealed bearings are used.
Every 50000 miles Change rear axle fluid (F-450/550 only).
(80000 km)
Every 60000 miles Change transfer case fluid (4WD vehicles).
(96000 km)
*
Vehicles equipped with dual rear wheels should rotate the front wheels
when specified; rear wheels only if unusual wear is noted.
2013 F-250/350/450/550 (f23)
Owners Guide gf, 1st Printing
USA (fus)
Dusty Roads
*
, inspect tires for wear and measure
407