What do I do about engine oil?

Chevy oil life gauge is reliable. If you have the manual your vehicle came with, it should list the type of oil it needs. Go with a well-known brand like Chevron for the additive. It's good for cars that have been sitting around for a while, otherwise you won't really notice any difference. Keep in mind that most premium grade gasoline already has a cleaner additive in it and to maintain your fuel system it is more than sufficient to add a separate additive every other month.