In terms of maintenance, the most cost-effective task for improving fuel economy is keeping your tires inflated to their recommended pressure level; any gain is not likely to be dramatic.
The federal Department of Energy/EPA fuel economy website, Fueleconomy.gov , says under-inflated tires can lower gas mileage by as much as 3.3 percent. Air is cheaper than gas, so it pays to keep tires inflated to what the manufacturer recommends on the tire placard typically found on the driver's doorjamb and in the owner's manual.
Tire choice also can improve fuel economy. You have to stick with the size and, to some extent, the type of tire specified by the vehicle manufacturer (such as performance versus all season), but when it's time to replace tires you should investigate what alternatives are available. For example, if your SUV is equipped with knobby off-road tires designed for slogging through mud and gravel but 98 percent of your driving is on paved roads, you could switch to all-season tires with a smoother tread and low rolling resistance that can improve fuel economy.
Some SUV and pickup owners obviously love the monster-truck look that comes with massive tires, but they are spending extra cash at the pump for that look.
No matter what you drive, when you shop for tires you should look for those described as having low rolling resistance or fuel-saving technology.
Don't ignore a check engine light or other warnings involving the emissions system because those are often indications that a component of the emissions and/or fuel system has failed. A faulty sensor can send incorrect signals to the computers that control today's engines, and that could result in unnecessary fuel consumption. The DOE and EPA estimate this could reduce fuel economy 4 percent on average and as much as 40 percent from a faulty oxygen sensor. With electronic ignition and computer controls, the traditional automotive tuneup is history. About the only tuneup-related items left are replacing the spark plugs and the engine air filter. Most vehicle maintenance schedules call for spark plugs to be replaced every 100,000 miles or more, and we aren't sure fresh ones will yield enough benefit to justify the cost. Engine computers do a remarkable job of compensating for worn plugs.
The DOE and EPA say a fresh air filter can improve acceleration 6 to 11 percent because of better air flow but won't have a noticeable effect on fuel economy.
Though this doesn't fall into the maintenance category, slowing down is a great way to save gas. We're all in a hurry at least some of the time, but the DOE and EPA say that avoiding jack-rabbit starts and staying within the speed limit can improve fuel economy 7 to 14 percent. On many urban expressways and interstate highways, doing the speed limit means you'll get a lot of dirty looks and maybe some unfriendly gestures from antsy motorists. But moving over to the right lane and slowing down a little should save some gas.