Before you begin
If you already own a car, there are several gas consumption factors which you can't control: engine size and design, vehicle weight and wind resistance, gasoline quality and formulation. There are, however, a few ways in which you are the master of your driving fate, so let's concentrate on those. All of the strategies boil down to two words: maintenance and driving habits.


Step 1: Maintain optimum tire pressure

It sounds like a no-brainer, but when was the last time that you checked your tire pressure? It takes more effort for an engine to propel an underinflated tire than a properly inflated one--the engine uses more gas to move it along.

The trickiest part of checking your tire pressure is that you actually have to check it twice: once before the vehicle has been moved that day, and again when you're at a gas station with an air hose. The first reading is from a cold tire, and it's the accurate one, while the second is from a tire that has warmed up from rolling on the pavement. Here's the routine:

Get a good quality tire gauge, and measure the pressure in all four tires before you move the vehicle. You'll do this by removing the plastic caps on your valve stems and pressing the gauge firmly down over the metal threads on the end of the stem. You'll hear a little hiss as a bit of air escapes, but when you press the gauge firmly down and hold it there, the noise will stop and the gauge will register the tire pressure.

Write down the measurement for each tire--this is your coldmeasurement. Tire companies specifications reflect cold tire pressures, and pressure is measured in PSI, or Pounds per Square Inch.

The auto manufacturer has specified tire pressures for both front and back tires. Look for these specs on the inside edge of the driver's door, on the inside of the glove compartment door, or in the owner's manual.

Compare the cold measurements with the manufacturer's pressure recommendations. If the manufacturer recommends a different pressure (either higher or lower) than the cold measurement, you'll adjust the tire pressure accordingly.

Find a service station with an air hose. There will either be a metal handle that releases air when you squeeze it, or a simple metal fitting that releases air when it's pressed over the valve stem.

Take the tire pressure again with your own tire gauge. It'll probably be a bit higher than the cold measurement, since the tire has warmed up from rolling along the pavement. This will be the warm measurement.

If the cold measurement was lower than the manufacturer's recommendation, add the proper amount of air with the hose.

On the other hand, if the cold measurement was higher than the manufacturer's recommendation, release the excess pressure from the tire. (This is easy to do: find the valve, and press on the metal piece in the center of the valve with your fingernail, a key, or a small stone, until your hear a hissing sound.

Overly inflated tires can wear unevenly, so don't try to overinflate them into balloons.


Step 2: Keep it in tune

Keep your engine tuned properly. Nowadays, most cars on the road have electronic ignitions that are simpler to maintain than they used to be, but there are still a few items that need attention.

• The air filter should be replaced when you can't easily see light through it.
  
• The timing should be properly adjusted.
  
• The spark plugs should be clean, gapped correctly and firing properly.
  
• Older cars and trucks may need the points replaced as well.
  
• Keep your exhaust system in good shape. A hole in your muffler or along your exhaust pipe will reduce your gas mileage as well as making noise and a bad smell.

Constant speeds, rather than speeding up and slowing down, help enormously. That's why highway gas mileage estimates are always higher than the estimates for around-town driving. If you can plan your route to avoid strings of traffic lights, stop signs or children's play areas, your gas mileage will definitely improve.

In most cars, the air conditioner draws power from the engine, using a belt. Every time that you turn on the air conditioner, the engine has to use more gas to keep the car moving. Although opening the windows can also reduce your gas mileage by reducing the aerodynamic efficiency, it's still better than running the air conditioner.

Overloading the car makes the engine work overly hard and consume extra gas. If you can split the luggage (or building supplies) between two vehicles, then do it. This doesn't mean, however, that you ought to take two cars when one car will suffice.

• A car
  
• A pen (or pencil) and paper