Ford F-250 Owner's Manual page 381

If you must replace the fuel filler cap, replace it with a fuel filler
cap that is designed for your vehicle. The vehicle warranty may
be void for any damage to the fuel tank or fuel system if the
correct genuine Ford or Motorcraft fuel filler cap is not used.
WARNING: The fuel system may be under pressure. If the fuel
filler cap is venting vapor or if you hear a hissing sound, wait
until it stops before completely removing the fuel filler cap. Otherwise,
fuel may spray out and injure you or others.
WARNING: If you do not use the proper fuel filler cap,
excessive pressure or vacuum in the fuel tank may damage the
fuel system or cause the fuel cap to disengage in a collision, which may
result in possible personal injury.
FFV (Flex Fuel Vehicle) fuel cap
If your vehicle is FFV capable, it will have a yellow colored fuel cap.
Choosing the right fuel
If your vehicle is a flexible fuel vehicle (FFV), use only UNLEADED
FUEL and FUEL ETHANOL (Ed75–Ed85).
If your vehicle is not a flexible fuel vehicle (FFV), then only use
UNLEADED fuel or UNLEADED fuel blended with a maximum of 10%
ethanol. Do not use fuel ethanol (E85), diesel, methanol, leaded fuel or
any other fuel.
The use of leaded fuel is prohibited by law and could damage your
vehicle.
Your vehicle was not designed to use fuel or fuel additives with metallic
compounds, including manganese-based additives.
Note: Use of any fuel other than those recommended may cause
powertrain damage, a loss of vehicle performance, and repairs may not
be covered under warranty.
Octane recommendations
Your vehicle is designed to use "Regular" unleaded gasoline with a pump
(R+M)/2 octane rating of 87. 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.
2011 F-250/350/450/550 (f23)
Owners Guide, 3rd Printing
USA (fus)
Maintenance and Specifications
381