A little math.
170 miles at 9mpg is about 18.5 gallons of gas
170 miles ar 11mpg is about 15.5 gallons of gas.
Net saving is 3 gallons. $2.50 / gallon is $7.50 saved.
Royal purple magic mix to get that savings... ~$12.......
Still lost money even if it did work to gain 2mpg