CHEVROLET 1999 Corvette - Manual (Page 264)

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D SAE 5W - 30
As shown in the viscosity chart, 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.
Oils meeting these
requirements should also
have the “Starburst” symbol
on the container.
This symbol indicates that the oil has been certified by
the American Petroleum Institute (API).
You should look for this on the oil container, and use
only those oils that are identified as meeting GM
Standard 4718M and have the Starburst symbol on the
front of the oil container.