Chevrolet 2007 Avalanche Owner's Manual page 446

Many service stations will not have an 85% ethanol
fuel (E85) pump available. The U. S. Department
of Energy has an alternative fuels website
(www.eere.energy.gov/afdc/infrastructure/
locator.html) that can help you find E85 fuel.
Those stations that do have E85 should have a
label indicating ethanol content. Do not use the fuel
if the ethanol content is greater than 85%.
At a minimum, E85 should meet ASTM
Specification D 5798.
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To ensure quick starts in the wintertime, the
E85 fuel must be formulated properly for your
climate according to ASTM specification D 5798.
If you have trouble starting on E85, it may be
because your E85 fuel is not properly formulated for
your climate. If this happens, switching to gasoline
or adding gasoline to your fuel tank may improve
starting. For good starting and heater efficiency
below 32°F (0°C), the fuel mix in the fuel tank
should contain no more than 70% ethanol. It is best
not to alternate repeatedly between gasoline and
E85. If you do switch fuels, it is recommended that
you add as much fuel as possible — do not add
less than five gallons (18.9 L) when refueling. You
should drive the vehicle immediately after refueling
for at least five miles (8 km).