What's the 2008 Chevy Impala SS oil type?

Your 2008 Chevrolet Impala is going to take 5 quarts of 5W-30 synthetic oil. While You could go with a traditional oil here, using a synthetic will last longer as it resists breaking down and handles high temperatures much more efficiently. You'll be able to go double the time You would with a conventional oil, and Your engine will actually perform better. A note on the viscosity level here, but if You live in a severely cold climate, You can bump it down to 0W-20; if You do this, though, You should go back to A5W-30 in the Spring time where You live.