Surveys show that 60 percent of the vehicles on the road have tires that are underinflated by at least 30 percent. That's at least 9 psi below the manufacturer's recommended pressure. That can cost you almost 7 percent in wasted fuel ($245 per year, or 24¢ per gallon). Plus, low air pressure causes premature tire wear, and that can cost almost $300 over the life of the tires. For best results, check your tire's air pressure with a digital pressure gauge (about $10 at any auto parts store) and fill to the recommended pressure shown on the decal inside the driver's door or on the driver's door pillar.
If your 100,000-mile spark plugs have 80,000 miles on them, they’re 80 percent worn. Misfires and incomplete combustion occur more frequently during that last 20,000 miles, costing you almost $562.50 in wasted fuel. You have to replace your spark plugs anyway, so do it early and pocket the savings. Even if you have to replace the plugs one extra time over the life of your car, you’ll still come out way ahead. And don't automatically assume your plugs are good for 100,000 miles. Many four-cylinder engines require new spark plugs at either 30,000- or 60,000-mile intervals.
Your engine sucks in 14 million gallons of air through the filter every year. On older vehicles (pre-1999) a dirty air filter increases fuel usage by almost 10 percent ($350 per year, or 35¢ per gallon). On newer vehicles, the computer is smart enough to detect the lower airflow, and it cuts back on fuel. So your engine will lack power and pick-up. Check the filter when you change your oil and replace it at least once a year, or more if you drive in dirty, dusty conditions.
If your tires are bowed out of alignment by just .017 in., it's the equivalent of dragging your tire sideways for 102 miles for every 20,000 you drive. That’ll cost you $187.50 a year in wasted gas. It will wear your tires faster, costing you $70 more a year.
Here’s an easy way to check your alignment without taking your car in to the shop. Buy a tread depth gauge ($2) and measure the tread depth on both edges of each tire (rear tires too). If one side of the tire is worn more than the other, your car needs to be aligned. An alignment costs about $80, so you'll still save $177.50 the first year alone.
The plastic air dam (aka “spoiler”) that’s broken or missing wasn’t just for a sporty look. If your car had an air dam, driving without it or with a damaged one can reduce your gas mileage. The air dam literally “dams off” airflow to the undercarriage of your car, forcing the air up and over the hood. That helps your car cut through the air with less drag. It also increases airflow to the A/C condenser and radiator, reducing the load on your car’s electrical system. Contact a junkyard or visit certifit.com to get a replacement air dam.
Yes, you’ve heard it before, but how about some real world numbers to drive the point home? Aerodynamic drag is a minor concern in city driving, but it really kills your gas mileage at speeds over 55 mph. In fact, increasing your speed to 65 increases drag by 36 percent! If you do a lot of highway driving, getting to your destination a few minutes early could cost you an extra $500 to $600 a year. Keep it closer to 55 mph and use your cruise control. It will pay off.
Oxygen sensors monitor the efficiency of combustion by tracking the amount of oxygen remaining in the exhaust. But they degrade over time and that can cost you up to 15 percent in gas mileage. When they fail, the computer lights up your "service engine soon" light, forcing you to incur an $80 diagnostic fee. On pre-1996 vehicles, replace your oxygen sensor every 60,000 miles to keep your mileage at its peak. On 1996 and newer vehicles, replace the sensors every 100,000 miles. Oxygen sensors cost about $60 each. Some vehicles have as many as four, but the sensors installed behind the catalytic converter rarely fail.