GMC CHEVROLET Silverado 6500HD 2019 Owner's Manual page 298

American Petroleum Institute (API)
Symbol
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.
Look for this on the oil container,
and use only those oils that display
this logo.
Caution
Use only engine oils that have the
designation CJ-4 or CK-4 for the
diesel engine. Failure to use the
recommended oil can damage the
DPF and result in engine damage
not covered by the vehicle
warranty.
Viscosity Grade
Use SAE 15W-40 viscosity grade
engine oil.
Vehicle Care
When it is very cold, below 18 °C
(0 °F), use SAE 5W-40 to improve
cold starting. These numbers on the
oil container show its viscosity,
or thickness.
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