Keep Your Engine Properly Tuned

Fixing a car that is noticeably out of tune or has failed an emissions test can improve its gas mileage by an average of 4 percent, though results vary based on the kind of repair and how well it is done.

Fixing a serious maintenance problem, such as a faulty oxygen sensor, can improve your mileage by as much as 40 percent.

Keep Tires Properly Inflated

You can improve your gas mileage by up to 3.3 percent by keeping your tires inflated to the proper pressure. Under-inflated tires can lower gas mileage by 0.3 percent for every 1 psi drop in pressure of all four tires. Properly inflated tires are safer and last longer. I usually add 5 psi more then recommended to get better mileage.

The proper tire pressure for your vehicle is usually found on a sticker in the driver's side door jamb or the glove box and in your owner's manual. Do not use the maximum pressure printed on the tire's sidewall.

Use the Recommended Grade of Motor Oil

You can improve your gas mileage by 1–2 percent by using the manufacturer's recommended grade of motor oil. For example, using 10W-30 motor oil in an engine designed to use 5W-30 can lower your gas mileage by 1–2 percent. Using 5W-30 in an engine designed for 5W-20 can lower your gas mileage by 1–1.5 percent. Also, look for motor oil that says "Energy Conserving" on the API performance symbol to be sure it contains friction-reducing additives.

NEW INFORMATION: Replacing a Clogged Air Filter on Modern Cars Improves Performance but Not MPG

A new study shows that replacing a clogged air filter on cars with fuel-injected, computer-controlled gasoline engines does not improve fuel economy but it can improve acceleration time by around 6 to 11 percent. This kind of engine is prevalent on most gasoline cars manufactured from the early 1980s onward.

Tests suggest that replacing a clogged air filter on an older car with a carbureted engine may improve fuel economy 2 to 6 percent under normal replacement conditions or up to 14 percent if the filter is so clogged that it significantly affects drivability.

The effect of a clogged air filter on diesel vehicles will be tested in the near future.

Note: Cost savings are based on an assumed fuel price of $3.87/gallon.

Drive Sensibly

Aggressive driving (speeding, rapid acceleration and braking) wastes gas. It can lower your gas mileage by 33 percent at highway speeds and by 5 percent around town. Sensible driving is also safer for you and others, so you may save more than gas money.

Let your car glide to a stop get your foot off the accelerator when approaching turns, heavy traffic and intersection or red lights. Just coast the car in for these stops.

Fuel Economy Benefit:	5–33%
Equivalent Gasoline Savings:	$0.19–$1.28/gallon

Observe the Speed Limit

While each vehicle reaches its optimal fuel economy at a different speed (or range of speeds), gas mileage usually decreases rapidly at speeds above 60 mph.

You can assume that each 5 mph you drive over 60 mph is like paying an additional $0.31 per gallon for gas.

Observing the speed limit is also safer.

Fuel Economy Benefit:	7–23%
Equivalent Gasoline Savings:	$0.27–$0.89/gallon

Remove Excess Weight

Avoid keeping unnecessary items in your vehicle, especially heavy ones. An extra 100 pounds in your vehicle could reduce your MPG by up to 2 percent. The reduction is based on the percentage of extra weight relative to the vehicle's weight and affects smaller vehicles more than larger ones. The new cars do not come with a spare tire.

Fuel Economy Benefit:	1–2%/100 lbs
Equivalent Gasoline Savings:	$0.04–$0.08/gallon

Avoid Excessive Idling

Idling can use a quarter to a half gallon of fuel per hour, depending on engine size and air conditioner (AC) use. Turn off your engine when your vehicle is parked. It only takes a few seconds worth of fuel to restart your vehicle. Turning your engine on and off excessively, however, may increase starter wear.

Fuel Cost Savings:	$0.01–$0.03/min. (AC off)
	$0.02–$0.04/min. (AC on)

Use Cruise Control

Using cruise control on the highway helps you maintain a constant speed and, in most cases, will save gas.

Use Overdrive Gears

When you use overdrive gearing, your car's engine speed goes down. This saves gas and reduces engine wear.