The car has been getting a very bad gas mileage. When I bought the car, I figured that the data on the dash need some mileage to provide accurate data. I checked the MPG manually and I've been getting around 20 on the highway, which should be up to 29 MPG for this make and model. Moreover, when I drive in the city traffic, I've been getting around 18 MPG, which again should be up to 24 MPG. That is a big difference. As for my driving style, I'm keen on acceleration but I don't drive violently so that cannot be the cause. At the dealership, they didn't get any error codes so they couldn't help me. They only told me that it might be caused by my installing the bike roof rack. But that is the Mazda OEM part and in any case, I had bad gas mileage even before I had that installed. Lately, I've been measuring the MPG both with the meter on the dashboard and manually and the data shown is accurate. Do you have some suggestion on how I could improve this horrible gas mileage? Is there any part that has gone bad that causes this?
I would do a little quick research and find out what is typical real-world MPG for others who drive your make and model. That will provide you a realistic base-line expectation that will be more accurate that Mazda or EPA estimates. Now to a few things that can hurt fuel mileage. The wind resistance from the rack will certainly make a difference. But more at highways speeds and less so around town at lower speeds. Tire inflation is a factor. Check them monthly and inflate as per door sticker. Your right foot is probably the biggest variable in all of this.
You could do an experiment! For one week drive like there is an egg between your right foot and the gas pedal. Your mission is to press very gently on the pedal so you don't break the egg! The results will indicate if your poor gas mileage is due to "enthusiastic" driving. I don't know if your Mazda has an automatic or manual transmission. If you have a stick shift and you regularly run it up to higher rpm's before shifting, that will use more gas. If I was looking at scan tool data for an engine performance problem that was hurting gas mileage, I would view fuel trims and misfire data after checking for diagnostic trouble codes (DTC's). If you would like to have this checked, a certified technician from YourMechanic can come to your home or office to diagnose the mileage issue.
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