You can but you gonna have problems after 300k and performence wise you would feel like driving a Toyota. If you put premimum theres less chances of repairs its a small difference
if its regular gas
It's physically possible to do so and the engine will run, but you shouldn't make a practice of it. The engine will run roughly and inefficiently. It will get worse over time.
Yes.
Regular.
Yes
Never put gas in a diesel car. And never put diesel in a gas car. An engine is built to handle one and not the other.
Regular unleaded.
Regular unleaded
Regular Unleaded.
" regular " unleaded , 87 octane
In order to preserve the motor in your CTS you should put only premium gas in it.
You will risk doing damage to the catalytic converter(s).