Ford 1996 Aerostar Manual page 254

Choosing the Right Fuel
Use only UNLEADED FUEL in your vehicle.
Using leaded fuel is prohibited by federal law.
Your warranty may not apply if your vehicle is
damaged because you used the wrong fuel.
Vehicle inspection programs may detect
misfueling. Under these circumstances, you may
be required by law to make costly repairs at
your own expense.
Octane recommendations
Your engine is designed to use regular
unleaded 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 on a label
on the pumps.
Typical octane rating label
In some parts of the country, "regular" grade
fuels are sold with octane ratings of 86 or even
less, especially in high altitude areas. We
recommend that you do not use these fuels.
Always use a fuel with an octane rating of 87,
even if it is sold as a "midgrade" or "premium."
Do not be concerned if your vehicle sometimes
knocks lightly when you drive up a hill or when
you accelerate. However, if a fuel with the
recommended octane rating knocks heavily
under all driving conditions or knocks lightly
driving at cruising speed on level roads, see
your dealer or a qualified service technician.
Persistent, heavy knocking can damage the
engine.
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