Fuel; Gasoline Octane; Gasoline Specifications - Cadillac 2008 XLR Owner's Manual

Fuel

Use of the recommended fuel is an important part of the
proper maintenance of your vehicle. To help keep the
engine clean and maintain optimum vehicle performance,
we recommend the use of gasoline advertised as TOP
TIER Detergent Gasoline.
The 8th digit of the Vehicle Identification Number (VIN)
shows the code letter or number that identifies your
vehicle's engine. The VIN is at the top left of the
instrument panel. See Vehicle Identification Number
(VIN) on page 6-89.

Gasoline Octane

If your vehicle has the 4.6L V8 engine (VIN Code A),
use premium unleaded gasoline with a posted octane
rating of 91 or higher. You can also use regular
unleaded gasoline rated at 87 octane or higher, but
your vehicle's acceleration could be slightly reduced,
and you might notice a slight audible knocking noise,
commonly referred to as spark knock. If the octane
is less than 87, you might 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
could damage the engine. If you are using gasoline
rated at 87 octane or higher and you hear heavy
knocking, the engine needs service.
If your vehicle has the 4.4L V8 engine (VIN Code D),
use premium unleaded gasoline with a posted
octane rating of 91 or higher. For best performance,
use premium unleaded gasoline with a posted octane
rating of 93. In an emergency, you can use regular
unleaded gasoline with an octane rating of 87 or higher.
If 87 octane fuel is used, do not perform any aggressive
driving maneuvers such as wide open throttle
applications. You might also hear audible spark knock
during acceleration. Refill the tank with premium fuel
as soon as possible to avoid damaging the engine.
If you are using gasoline rated at 91 octane or higher
and you hear heavy knocking, the engine needs service.
Gasoline Specifications
At a minimum, gasoline should meet ASTM specification
D 4814 in the United States or CAN/CGSB-3.5 or
3.511 in Canada. Some gasolines contain an
octane-enhancing additive called methylcyclopentadienyl
manganese tricarbonyl (MMT). We recommend
against the use of gasolines containing MMT.
See Additives on page 6-6 for additional information.
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