Mercury 1996 Cougar Manual page 233

Octane recommendations
Your engine is designed to use 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.
Using a fuel with a lower octane rating can
cause persistent and heavy knocking, which can
damage the engine.
Do not be concerned if your vehicle sometimes
knocks lightly when you drive up a hill or when
you accelerate. However, see your dealer or a
qualified service technician if persistent heavy
knocking occurs because this can damage the
engine.
If your vehicle has problems with starting, rough
idle or hesitation problems when the engine is
cold, it may be caused by fuel with low
volatility. Try a different brand of fuel. If the
condition persists, see your dealer or a qualified
service technician.
Gasolines for clean air
Fuels in certain areas of the country are required
to contain oxygenates to improve air quality.
Common oxygenates are ethanol or grain alcohol
(blended at no more than 10%), methanol or
wood alcohol (blended at no more than 5% with
cosolvents and additives), and MTBE or methyl
tertiary butyl ether (blended at no more than
15%).
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