Our 2012 Prius recommends using the regular stuff. We’ve never really used the lower grades, unless for some reason the gas station was out of premium. Some people have experienced Prius cold start engine knock possibly due to engine crud being pushed back into the engine via EGR. Solution for them, oil catch can. Not us, at least so far....
Can anyone say Anti-Knock Index? (AKI)
Can anyone say Anti-Knock Index? (AKI)