Because I've been hearing this since the car was brand new, I've contemplated the thought of whether the full tank of gas the car came with was filled with regular gas or something. Every fill up I've done myself has been with premium gas. The car has about 700 miles on it, and I get about 150 miles per fill up, so that's like 4-5 fills with premium since the dealer did their first fill up..

The reason I immediately started contemplating whether the dealer used the right gas or not it because when I had a mazdaspeed3, the salesmen put 87 in it in front of my own eyes.. And I realized what he had done when it was already full..