Our 2 cars use unleaded gasoline which is cheaper by about 5% than the premium gasoline. But some people, including the gas station attendant, advise us to use premium gasoline instead in order to save on power. The unleaded is cheaper but it gives less power and as per their computation on the mileage, premium gasoline covers more distance in the same amount (or money and not in liters). But we have a hesitation on the issue because the gas tank's cap clearly say "unleaded gasoline only." What happens if something goes wrong with the engine? What is your opinion on this?