Mercury Sable 1999 - Manual (Page 161)

Your vehicle was not designed to use fuel or fuel
additives with metallic compounds, including
manganese-based compounds containing (MMT).
Repairs to correct the effects of using a fuel for
which your vehicle was not designed may not be
covered by your warranty.
Octane recommendations
Your vehicle is
designed to use
“Regular” unleaded
gasoline with an
(R+M)/2 octane rating of 87. We do not recommend
the use of gasolines labeled as “Regular” that are
sold with octane ratings of 86 or lower in high
altitude areas.
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 dealer or
a qualified service technician to prevent any engine
damage.
Fuel quality
If you are experiencing starting, rough idle or
hesitation driveability problems during a cold start,
try a different brand of “Regular” unleaded gasoline.
“Premium” unleaded gasoline is not recommended
(particularly in the United States) because it may
cause these problems to become more pronounced.
If the problems persist, see your dealer or a qualified
service technician.
It should not be necessary to add any aftermarket
products to your fuel tank if you continue to use a
high-quality fuel.
Cleaner air
Ford approves the use of gasolines to improve air
quality, including reformulated gasolines that contain
oxygenates up to 10% ethanol or 15% MTBE.
87
(R+M)/2 METHOD
Maintenance and care
161