FORD 2013 F-550 v.3 - Manual (Page 192)

Choosing the Right Fuel With a Flex Fuel Vehicle (If Equipped)
Note: If your vehicle is FFV capable, it will have a yellow colored fuel cap.
Flex fuel vehicles are designed to use only ethanol fuel blends which
contains 51 to 83% ethanol and UNLEADED FUEL Regular unleaded
gasoline or any mixture of the two fuels.
It is best not to alternate repeatedly between gasoline and E85. If you do
switch fuels, it is recommended that you add as much fuel as possible—at
least half a tank. Do not add less than five gallons (18.9 liters) when
refueling. You should drive the vehicle immediately after refueling for at
least 5 miles (8 kilometers) to allow the vehicle to adapt to the change in
ethanol concentration. If you exclusively use E85 fuel, it is recommended
to fill the fuel tank with regular unleaded gasoline at each scheduled oil
change.
Octane Recommendations
Regular unleaded gasoline with a
pump (R+M)/2 octane rating of 87 is
recommended. Some stations offer
fuels posted as Regular with an
octane rating below 87, particularly
in high altitude areas. Fuels with octane levels below 87 are not
recommended.
Regular unleaded gasoline with a pump (R+M)/2 octane rating of 87 is
recommended. Some stations offer fuels posted as “Regular” with an
octane rating below 87, particularly in high altitude areas. Fuels with
octane levels below 87 are not recommended.
Do not be concerned if your engine sometimes knocks lightly. However, if
it knocks heavily under most driving conditions while you are using fuel
with the recommended octane rating, see your authorized dealer to
prevent any engine damage.
87
(R+M)/2 METHOD
Fuel and Refueling 191
2013 F-250/350/450/550 (f23)
Owners Guide gf, 3rd Printing, December 2012
USA (fus)