Why is my minivan's gas mileage so bad?

Nancy’s Question: "Why am I getting such poor gas mileage from my minivan?"

There are many factors that can contribute to poor gas mileage, but before we talk about them, we need to make sure that people understand how to accurately calculate their gas mileage. Start at the gas pump by filling up your tank until the pump shuts off. Don’t “top off” or try to get extra gas into the filler neck, this is dangerous and will also distort your mileage measurement. Next, record the exact mileage on the odometer after filling. Drive as you normally do until you are below one quarter tank of fuel. Fill the fuel tank the same way you did last time, without “topping off”, and record the exact gallons and tenths pumped. Record the current mileage on the odometer, and subtract the previously recorded mileage. This is the mileage driven on the amount of fuel you just pumped. Divide the mileage by the gallons and that is your fuel economy for this tank.

Now let’s look at how you can improve that mileage. Basically, fuel economy is affected by some factors you can’t control (engine size, gasoline quality, wind drag), and some you can control. We will focus on what you can control – maintenance and driving habits. One of the most common causes of poor gas mileage is under inflated tires. Make sure your tires are filled to the manufacturers recommended pressure, and check them often; at least once a month. Another common cause of bad gas mileage is a dirty air filter. If you can’t easily see daylight through yours, it needs to be replaced. Make sure you follow all of the manufacturers maintenance recommendations under the severe service schedule in your cars owners’ manual, including spark plug replacement when it’s needed. Finally, changing your driving habits may well have more impact on fuel economy than any other single factor. The faster you drive, the more gas you burn. Slow down to the speed limit for starters. Heavy acceleration and hard braking also waste gas – accelerate slowly from traffic lights and brake slowly and evenly at stops. Also keep in mind that every minute spent sitting at idle results in zero miles per gallon for the fuel you use during that time. Reduce idling by going into the restaurant if there are more than one or two cars in the drive-through, and if you’re waiting for someone, shut the car off.