GMC TopKick 2007 Owner's Manual page 271

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SAE 15W-40
As shown in the viscosity chart, SAE 15W-40
is best for your vehicle. However, you can
use SAE 10W-30 at temperatures above
0°F (−18°C). When it is very cold, below
0°F (−18°C), you should use SAE 5W-40
to improve cold starting. 5W-40 is not
recommended for use at high temperatures,
above 100°F (38°C).
These numbers on the oil container show
its viscosity, or thickness. Do not use other
viscosity oils such as SAE 10W-40 or
SAE 20W-50.
You should look for this on the oil container, and
use only those oils that display this logo.
This doughnut-shaped
logo (symbol) is used on
most oil containers to
help you select the
correct oil. It means that
the oil has been certified
by the American
Petroleum Institute.
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