Ford 1996 Taurus Manual page 263

If you do not use the proper fuel cap, the
pressure in the fuel tank can damage the
fuel system or cause it to work improperly
in a collision.
NOTE: If you replace your fuel cap with an
aftermarket fuel filler cap, the customer
warranty may be void for any damage
to the fuel tank and/or fuel system.
Choosing the Right Fuel
Use only UNLEADED FUEL. Using leaded fuel
is prohibited by federal law. Any vehicle
damage may not be covered by your warranty.
Octane Recommendations
All models except SHO 3.4L
Your vehicle is designed to use regular fuel
with an octane rating of 87. In most cases it is
not necessary to use a fuel with an octane rating
higher than 87. At service stations, the octane
rating is displayed in a label on the pumps.
Typical octane rating label
We do not recommend gasolines labeled
"regular" that are sold with octane ratings of 86
or even less in high altitude areas.
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