I answer a lot of questions on Quora. Many of those questions are about automotive things that may be of interest to CarNewsCafe readers. Like this one.
My Answer: There are three possible reasons for this: your car has a problem, you aren’t driving with MPG in mind, or your car’s configuration is not the same as that used for the EPA’s testing.
The most likely problem is you, but lets look at the car first. Common issues that cause lower MPG (especially in town) are emissions clogs (usually the mass airflow sensor or bypass), dirty filters, low-grade gasoline, low tire pressure, or a combination of these things.
If you’re pumping E85 gasoline, understand that the ethanol in it makes it less efficient than pure gasoline. EPA tests are done with no ethanol in the fuel, usually with 91 octane. Your vehicle loses up to 4% of its fuel efficiency when 15% ethanol (E85) is used instead of pure petroleum.
Emissions systems can become clogged, though your vehicle is new enough that this is very unlikely to have happened. Sensors can get gummed up and not trigger an engine repair code (OBD code and resulting light on the dash). Likewise, dirty filters can restrict airflow and cause the engine to work harder to get the same amount of energy out, which reduces fuel economy. Low tire pressure causes losses as well, though that usually manifests on the highway unless pressures are VERY low. These should set off tire pressure warnings on the gauge cluster.
Your car’s configuration, including how much stuff is on board (passengers, gear) and how much has been done to modify it (adding a luggage rack, bicycle mount, whatever), can affect its MPG returns. Sometimes drastically.
The most likely issue is your driving style. If you’re prone to tailgating, press the accelerator hard out of every light, slamming the brakes, using jerky movements to turn or maneuver, etc. then you’re directly affecting your fuel economy. Slower, smoother, more deliberately passive driving is far more conducive to good MPG returns.
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