Originally posted by iwannabenz
How about the reverse, any adverse effects on the engine if you throw a tank of premium in every once in a while in an engine that only normally requires "regular" (87 octane)? Better performance? Shortened engine life? No difference?
Generally, no! The difference between regular and premium grade fuel is octane. All commercial gasolines have deposit control and other additives, though some premiums might have a higher than minimum dose.
In California the blending of fuel, including additives in regulated and the only functional difference is octane.
Sometimes an engine tuned for regular might feel a bit smoother on premium especially when accelerating at half to 3/4 throttle from low revs. This is usually because on regular, the engine is detonating marginally - not enough to actually hear. Modern engines with knock sensors are set up to operate on the ragged edge of detonation, because this operating condition yields the best torque and fuel efficiency.