Hey there,
I recently purchased a 2010 Mazda CX-7 Grand Touring, (2.3L turbo).
I know that these aren't as reliable as honda's and toyotas, but it was at a great price and had under 55k miles on it.
As soon as I drove it off the lot I noticed that my gas mileage was averaging around 15Mpg. It's a heavy SUV and Im used to driving smaller more powerful cars so I tried to adapt my driving style to the point where I propably am driving the same way my grandmother does. Still I am getting awful fuel economy. Ontop of this, the car reccomends premium so I switched, thinking this may be the issue, but now im around 16-17Mpg. The car is rated at 17-25 and my 16-17 is combined 50/50 city/highway. The dealer replaced the spark plugs, brake pads, and oil etc, and I replaced the air filters and even reset the computer (which it then proceeded to roughly idle for a couple hundred miles). There are no codes on the computer and its in fantastic shape otherwise but this is one thing that is starting to drive me crazy. Any suggestions? Am I missing something?
(I live in the Miami area, so AC is on year round, though it's january so its only been in the 70's and havent been using the ac that much, so I worry the mileage will struggle even more during the hotter months, hopefully I can find some sort of way to improve before then)
The dealer replaced the spark plugs, brake pads, and oil etc, and I replaced the air filters
I don't know what the "etc." included so here is a list of some things that also decrease gas mileage:
dirty fuel injectors, dirty throttle body, dirty MAF(mass air flow) sensor, improper tire pressure, brand/type of tires. poor wheel alignment, winter gas blend, clogged catalytic converter...
MPG is directly related to engine speed. My 1999 Ford Ranger is EPA-estimated to get only 18 MPG highway, because I have aggressive gearing (it's got a 4.10 rear-end). I drive 60 MPH on the highway instead of 65. The engine speed it only 2100 RPMs. I routinely get between 19 and 22 MPG on the highway, depending on whether or not I hit stop-and-go traffic. Once, managed to get 23.5 MPG when gas prices hit $5 a gallon, lol. I drove at 55 MPH. The truck also has 293k miles on it.
Every time you double your speed, you consume 4x the fuel while traveling in the same gear. Anything over 65 MPH starts noticeably decreasing gas mileage in two ways. Run-of-the-mill cars and trucks are most efficient in the 60-65 range. Going faster means a lot more drag. The drag also increases with a square. If your car is traveling at 100 MPH, the car is experiencing 4x more drag than it was going 50 MPH. Your car is also moving at an engine speed of 3500 RPMs, or more, which is a double whammy for on gas mileage.
Keep your car under around 2100 RPMs while cruising, and see what that does.
The car is rated at 17-25 and my 16-17 is combined 50/50 city/highway.
Sometimes these small turbocharged engines won't get decent gas mileage. "up to 18 city, 25 hwy" (using premium gas) was Mazda's claimed EPA rating and you're at 15 mpg.. check you fuel trims, live data, see if something's off there. In your case where premium fuel achieves the best mpg, regular saves money but with even worse mpg.
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