Bad Gas Mileage on Highway 2008 Mazda 3 Hatchback
 

Hi, my boyfriend and I recently purchased a 2008 Mazda 3 hatchback. It has a 2.3 liter engine. Its gas tank is 14.5 gallons and it is supposed to get 22 mpg in the city and 29 mpg on the highway. The gas mileage seems to be okay in the city but on the highway it seems to go through more gas than it should. We drove to lansing and back which is about 40 miles there and 40 miles back taking the highway all the way there and back. When we got home we had like 2 notches above half a tank. That means it used like 6 gallons of gas when it should have only taken like 4 gallons of gas. Also, when driving on the highway it rides at 3,000 rpms. What could be causing it to use a lot of gas on the highway? Could it just be because it has a smaller engine?

I assume it's an automatic not a manual car. See 2008 Mazda 3 MPG - Actual MPG from 600 2008 Mazda 3 owners and https://www.carsguide.com.au/car-reviews/mazda-3-56549 Poor fuel economy (and noise) is a common complaint with this model. It's about the gearing and number gears in the transmission (4 speed auto or 5 speed manual) . Mazda addressed this issue in the later BL with a lighter engines and improved and lighter gearboxes with both 6 speed automatic and manual gearboxes that reduced the gearing at highway speed). But check it is going into 4th gear (watch the tacho for gear changes).