I grew up in a family that filled its vehicles with the cheapest "regular" gasoline, rather than "midgrade" or "premium". Recently, a mechanic suggested to me that I can get better mileage on the higher grade gasoline, and occasionally filling up with the "premium" gasoline is also good for cleaning out the engine. Is there any truth to this? How frequently should I be filling up with the "premium" gasoline in order to best utilize those cleaning benefits? Is there any research that actually suggests a difference in the mileage on different grades of fuel?
My car has 92000 miles.
My car has an automatic transmission.
Premium fuel should only be used if the manufacturer recommends it. You will see it printed on the fuel gauge if you are required to use it. All fuels sold in the USA have cleaners in the fuel now. Some name brands list different cleaners that they use and some name brands may be better than other in the cleaners they use but all have to meet minimum cleaning standards in the fuels. There is no need to use any fuel other than regular if that is all your car requires.