Cadillac 2007 CTS, Owner'S Manual, Page: 335 / 518

If your vehicle has the 6.0L V8 engine
(VIN Code U), use premium unleaded gasoline
with a posted octane rating of 91 or higher.
You may also use regular unleaded gasoline
rated at 87 octane or higher, but your vehicle’s
acceleration may be slightly reduced, and you may
notice a slight audible knocking noise, commonly
referred to as spark knock. If the octane is
less than 87, you may notice a heavy knocking
noise when you drive. If this occurs, use a gasoline
rated at 87 octane or higher as soon as possible.
Otherwise, you might damage your engine. If
you are using gasoline rated at 87 octane or higher
and you hear heavy knocking, your engine
needs service. Gasoline Specifications
At a minimum, gasoline should meet ASTM
specification D 4814 in the United States or
CAN/CGSB-3.5 in Canada. Some gasolines may
contain an octane-enhancing additive called
methylcyclopentadienyl manganese tricarbonyl
(MMT). General Motors recommends against the
use of gasolines containing MMT. See
Additives
on page 336 for additional information.
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