Pontiac 1999 Firebird - Manual (Page 263)

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6-15
5.7L V8 Engine
As shown in the chart, if you have the 5.7L V8 engine,
SAE 5W
- 30 is best for your vehicle. However, you can
use SAE 10W - 30 if it’s going to be 0
_F ( - 18
_C) or
above. These numbers on an oil container show its
viscosity, or thickness. Do not use other viscosity oils,
such as SAE 20W
- 50.