How to Drive Economically


It's no secret that the price of energy has been rising recently. Anyone who has put gas in a car lately has run into that fact. If you'd like to save money on gas, this article will offer tips on how to drive economically.

Keeping your vehicle in good shape can help with its fuel efficiency. Even simple things like dirty air filters, excessive exhaust emissions, and underinflated tires can combine to reduce fuel economy by as much as 25 percent.

Routine maintenance on a modern vehicle is relatively easy. Electronics and computerized systems mean there's less to tune and that intervals between servicing are surprisingly longer.

For example, spark plugs that used to need changing every 10,000 miles now can go 30,000 or even 50,000 miles before needing to be changed. The following tips can help your car become more fuel efficient.

Starting on the next page, we'll take a look at steps you can take to maintain your vehicle for fuel economy.

 

Improve Your Car's Aerodynamics

Don't Carry More Than You Need

Keep the car as light as reasonably possible. For each 100 pounds of extra weight, gas mileage is reduced by as much as 4 percent. Limit the everyday items in your trunk or cargo area to the bare necessities, which should include some emergency items, such as a small jug of water, a flashlight, and a few tools.

Don't haul around what you won't be using. Leave the golf clubs at home until you head for the links. Not only does extra bulk add fuel-gulping weight, but it can also upset your vehicle's normal weight distribution. That will impair handling and can even rob a front-wheel-drive car of valuable traction. If you must carry heavy items, try to put only a few of them inside the car at a time.

Remove That Rack

Wind drag increases fuel consumption. Get rid of anything that disturbs the smooth flow of air over your vehicle's surface. Most roof racks have removable cross members, and some racks can be removed altogether; take off your car's rack if it isn't in use. When you do need to carry something on the roof, keep it light and small -- both for fuel-saving aerodynamics and to avoid the risk of a top-heavy weight imbalance.

That grille bar and those running boards may make your SUV look rugged, but they also add weight and drag. And that bolt-on trunk-lid spoiler that makes you feel fast and furious? It's designed to harness the wind and press your car to the pavement at high speeds. The result is better grip on the road, but this "downforce" is actually artificial weight that hurts fuel economy. Worse, unless you are a racing technician versed in aerodynamics, chances are excellent that your spoiler isn't doing anything more than adding wind drag and weight. That's costing you at the pump, too.

Retain That Tailgate

Some pickup-truck drivers take it as an article of faith that they're saving fuel by driving with the tailgate down, or removed, or replaced by a mesh fabric or metal gate. False.

Aerodynamic studies show a pickup truck is most fuel efficient with its tailgate up. It seems the upright tailgate causes air flowing over the roof of the cab to collect as a stagnant "dome" in the cargo bed. As speed builds, this dome, which tapers in a teardrop shape near the tailgate, acts as an aerodynamic ramp that forces airflow over the tailgate, to the benefit of fuel efficiency.

Disrupt this flow by dropping or removing the tailgate, and air coming over the cab is left to swirl around in the cargo bed, degrading the truck's aerodynamics and hurting fuel economy.

Inflate Tires Properly

Proper tire inflation is critical to fuel economy, and to safety. Underinflated tires cause vehicle drag and increase fuel consumption. They also compromise handling ability in turns and in emergency maneuvers. They increase stopping distances and decrease control during braking. Under-inflation puts undue stress on tire sidewalls and also causes rolling tires to build and retain heat rapidly. Stress and heat are prime contributors to tire failure, including blowouts at high speed. Underinflated tires also wear down more quickly.

Properly inflated tires are harder and roll more easily. That helps fuel economy and improves tire life. It allows the treads to grip well in all conditions, including rain and snow. And properly inflated tires are able to work with your vehicle's suspension to provide maximum handling, steering, and braking ability.

An estimated four out of ten vehicles on the road have at least one underinflated tire. Pressure that's 3 pounds per square inch (psi) below the recommended reading may reduce gas mileage by 1.5 percent. Some experts suggest even greater decreases. The Environmental Protection Agency (EPA) warns that running tires at 20 psi or lower can easily cost you a full mile per gallon.

Proper Tire Inflation

Tires can naturally lose up to 1 psi every 30 days, and they will lose pressure more quickly in cold weather. Because cooler air is more dense, pressure drops by about 1 psi for every 10 degrees. A tire inflated to 30 psi at 70 degrees, for example, could drop as low as 26 psi at the freezing point.

The recommended tire pressure is displayed in your vehicle, typically on a sticker inside the glove box door or on one of the doorposts. It's also in your owner's manual. Many vehicles are available with a choice of tire sizes, and each size may have its own recommended inflation pressure.

Match the tire size as listed on the tire sidewall with that on the sticker or in the owner's manual. Note that the inflation number listed on the tire sidewall itself shows the maximum inflation, not the optimal pressure as determined by the tire maker and the manufacturer of your vehicle.

Checking Tire Inflation

Check inflation when the tires are cool. That means they have been driven less than a mile or so. Air expands inside a warm tire, which will give you a false reading.

Tire pressure should be checked at least every 30 days. A tire gauge is the old standby. But federal regulations require that by 2008 all new cars, sports utility vehicles, minivans, and pickup trucks be equipped with an underinflation warning system. Sensors will monitor tire pressure, and if it falls 25 percent below the recommended inflation, a yellow warning light on the dashboard will illuminate.

The system will save an estimated 120 lives and prevent 8,400 injuries annually, according to the National Highway Traffic Safety Administration. NHTSA estimates it will also save drivers up to $35 annually because of longer tread life and decreased fuel costs. Select 2004 and 2005 models already have such a system. For the 2006 model year, 20 percent of new vehicles must have the system, with 70 percent for 2007, and 100 percent for 2008.

Fuel Economy Varies with Tire Type

Those all-terrain or off-road tires with their knobby tread look rough and ready and are designed to get you through rocks and mud. They are not designed to promote high gas mileage.

All-season tires produce less friction and therefore roll more freely to the benefit of fuel economy. They're generally lighter than all-terrain or off-road tires, and less weight means better fuel economy. They also ride more quietly, handle better, and wear longer.

Maintaining Your Vehicle

Schedule Regular Maintenance

Cars that start quickly, run smoothly, and are in good mechanical condition get the best gas mileage. Whatever cuts into performance hurts economy. Scheduled maintenance also helps make parts last longer, so you save money two ways: today in economy, tomorrow in reduced repair costs.

A tune-up can boost fuel economy up to 10 percent, says the EPA. On modern fuel-injected cars equipped with computer-controlled powertrain systems, there's actually little to "tune up." Basically, today's tune-up means replacing the spark plugs, although it's also important to perform the kind of preventive maintenance described later in this section.

Follow The Schedule

Your owner's manual will likely list two maintenance schedules: one for "ordinary" driving; the other for "severe" or "heavy-duty" use. Each has its own maintenance program and lists the systems to be checked and the work to be done based on both mileage and time elapsed between servicing.

Even if you don't tow a trailer or drive in dusty conditions, your "ordinary" use can fall into the heavy-duty category if you live in a region subject to very hot or very cold temperatures. Even driving your vehicle on frequent short trips counts as heavy-duty use.

When in doubt, err toward the stricter maintenance schedule. It'll pay off in fuel savings weekly, and in long-term reliability.

Emissions and Fuel Economy

Exhaust emissions should be checked at least yearly for older vehicles. The lower a car's tailpipe emissions, the more efficiently its engine is operating.

Bringing your car's emissions down to within specifications can improve gas mileage as much as 15 percent. And your engine will last longer, too. The oxygen sensor is a key part of your emissions system, and some estimates suggest that a faulty oxygen sensor can reduce fuel economy by as much as 40 percent.

Under federal law, most emissions controls are covered by the factory warranty for 5 years or 50,000 miles. And some emissions-related repairs may be covered at no cost to you.

Look, Listen, and Sniff

Be alert for anything odd. Open the hood and look for loose wires or hoses. Check fluid levels regularly, as described later in this section. Be aware of any sudden drop in fuel economy or a curious odor. Monitor the coolant-temperature gauge, if your vehicle has one. As we'll see, running too cold costs fuel. Take note of any pinging or odd noises, hard starting, or significant loss of power.

In the next section, we'll discuss some simple do-it-yourself gas-saving maintenance that can increase your vehicle's fuel efficiency.

Additional Maintenance Tips

Proper maintenance can help your vehicle function more efficiently. Here are some do-it-yourself maintenance tips to keep your car in top fuel-economy shape.

Know What's Under the Hood

For economy's sake, you should know a little something about what's going on under the hood. Though undeniably complex and computerized, the principles of engine operation haven't changed as much over the years as many believe. Even if you don't do the work yourself, a bit of knowledge goes a long way when communicating with your mechanic and in making sure all the scheduled maintenance gets done.

Read About Your Vehicle

We're not talking manuals with instructions on replacing your transmission. And, for better or worse, modern vehicles don't afford too many do-it-yourself opportunities.

But there are many books, brochures, and videotapes that can help you get some basic insight into the purpose and workings of your vehicle. Examine these materials before you buy, however, and be sure they are aimed at your skill level and are current with the systems on your vehicle.

Don't overlook the automaker's shop manual for your car. Though written primarily with factory-authorized mechanics in mind, it contains plenty of useful information to guide the experienced do-it-yourselfer.

Check and Change the Oil Regularly

Oil is the lifeblood of your vehicle's engine, and maintaining proper oil levels and fresh oil will help keep your engine healthy and operating most efficiently. That leads to gas savings.

Check the level on the dipstick weekly. The oil should be checked with the engine turned off. The best time to get an accurate reading is when the engine is cold and the oil is pooled in the oil pan rather than dispersed throughout the engine's oil passages.

Always use the correct oil viscosity, as outlined in your owner's manual. The viscosity is described as 5W30 or 10W40, for example, and is a measurement of the oil blend's ability to do its job within a particular range of conditions and temperatures.

Using the incorrect viscosity can lower fuel economy by up to 2 percent. Any oil that carries an American Petroleum Institute (API) certification is appropriate. The API also monitors for friction-reducing additives and applies the term "Energy Conserving" to its performance symbol on motor oils that meet this standard.

Some synthetic motor oils are advertised as promoting fuel savings, though the advantage is generally negligible compared to simply changing your oil and filter regularly. Some tests have shown that synthetic oils result in slightly improved fuel economy, though their primary purpose is for use in high-performance engines as part of the total performance package. Synthetic oils are quite a bit more expensive than regular oil.

It's become fashionable to change your engine's oil and oil filter every 3,000 miles. It won't hurt to keep to that schedule, though evidence that it's a bit of overkill is in every owner's manual. Most manufacturers specify 15,000 miles or so between oil changes. They built the engine and should know what it needs to stay in top shape.

Some vehicles even have an oil-life monitor that will announce via a dashboard light when an oil change is necessary. This keeps track of how the vehicle is driven between oil changes and recommends when the oil should be changed.

If the manufacturer's oil-change schedule is outlined in the owner's manual or announced on a dashboard light, we recommend that you follow it.

Change the Air Filter

Some experts say not to expect a huge mileage boost from keeping your engine's air filter fresh; others say a clogged air filter can reduce gas mileage by as much as 10 percent.

In any case, changing an air filter is a simple task you can perform, and a properly operating air filter is essential for keeping the engine clean inside. A clogged or really dirty air filter cuts off air to the engine, and there's no doubt that hurts performance and fuel economy.

Maintain the Cooling System

An engine that runs too cool or too hot may waste 10 to 15 percent of the fuel you put into your gas tank. Your engine's operating temperature is governed primarily by the coolant fluid and the engine's thermostat.

Coolant is a blend of antifreeze and water that helps maintain proper engine temperature in both hot and cold weather conditions. The proper coolant blend is usually a 50-50 mix of antifreeze and water. The level should be maintained as indicated on the underhood reservoir, and the coolant should look clean.

A malfunctioning thermostat might stick open, which lengthens engine warm-up time and lowers the operating temperature, both of which hamper gas mileage. It could also stick in the closed position, which can cause the engine to overheat. Watch your dashboard coolant temperature gauge as a guide. Even if your car has no gauge but a warning light, one way to discover a malfunctioning thermostat is to pay attention to your car's heater. If it isn't delivering warm air within five minutes, even in freezing weather, get that thermostat checked.

Check Belt Tensions

Belts that drive the air conditioner, water pump, and power-steering pump must be tight enough not to slip, but not so tight as to bind. A rule of thumb used to suggest that belts needed a half-inch of slack, but some of today's engines are more delicate. Their belts must be checked by following the manual's instructions exactly, possibly using a measuring instrument to get tension exactly right. In any case, don't forget to shut off the engine before putting your hand anywhere near a belt.

Inspect the Battery

Batteries used to demand water periodically, but most of today's batteries are maintenance-free. What you can still do is inspect the cable terminals for corrosion and cleanliness. That can make the difference between getting an engine to start quickly and wasting gas while the engine cranks over too slowly -- or not at all.

Consider an Engine Block Heater

Motorists in the south may never give a moment's thought to such a device, but people in the north know this one well. Many of their cars have a little telltale plug sticking out of the grille. Connect it to ordinary house current and the crankcase stays warm overnight. Not only does the engine turn more freely in the morning, but it also warms up faster and wastes less fuel during that crucial period.

Pay Attention to the Brakes

Take note of suspicious symptoms. A dragging brake is not only dangerous but can also drag gas mileage down with every rotation. Brake maintenance is best left to an experienced mechanic. However, if you feel comfortable putting a corner of your car on a jack, as though you're changing a tire, give the wheel a spin to see if anything seems to be dragging. If it is, contact your mechanic. And make sure the parking brake is never left engaged when you start the car.

Maintain Wheel Alignment and Tire Balance

Professional equipment is needed to check these, but a misaligned front end or unbalanced tire can rob plenty of mileage. Is the car pulling to the side? Chances are a realignment is needed. Unless front wheels are pointing ahead properly, the tires might scrub against the pavement and steal fuel by straining the engine. Vibration at various road speeds suggests the need for balancing. An unbalanced tire also soaks up excess gas.

Steer Clear of Gimmicks

If there really were a device that could be added to an engine to yield 100 miles per gallon, it would be front-page news.

Gimmicks claiming to boost gas mileage -- a fluid or a gadget of some sort -- pop out of the woodwork whenever fuel supply or fuel costs become an issue. These tend to bear a startling resemblance to the "miracle cures" promised by medical charlatans.

The EPA has evaluated more than 100 such "amazing devices" over the years. A half-dozen produced a "statistically significant increase in fuel economy," and a couple of others did so only by increasing emissions levels. Recall the basic money-saving maxim: If it sounds too good to be true, it is.

Be especially wary of extravagant claims for phenomenal mileage, enhanced power, revived performance, and reduced emissions -- often all at the same time.

In addition to the questionable fuel and oil additives that promise miraculous mileage, many other additives are produced by reputable companies and sold at auto parts stores. Useful? Depends on who you ask.

Some experts steer clear of chemicals completely. Others allow that the occasional can of fuel-injector cleaner in the tank might help keep the injectors clean. Gas-tank additives can also absorb water that comes in with the latest fillup. Neither result has a direct effect on mileage, however. Basically, a car that's filled with high-quality brands of gasoline and oil shouldn't need any additives to keep it running properly.

Proper trip planning can help you use less gas and save some green at the pump. Next, learn about trip planning for energy efficiency.

Planning Your Route

Planning and modifying where you drive and how you get there can make a big difference in the number of times you have to stop for fuel every week.

What's the point of leaving the house half a dozen times in the course of a day when a little planning will allow you to do everything in one or two trips?

Particularly in winter, short trips are hard on an engine, which might never fully warm up. Cold engines guzzle a lot more fuel than properly warmed engines.

Drive to the farthest locale first, so the engine completely warms up before you shut it off. Stop-and-go driving with a cold engine puts an even greater strain on its parts.

Drivers who use their cars for business can also learn to plan their trips for the shortest total distance and greatest efficiency, as can families planning medical appointments and school activities. The following guidelines can help you plan your route for any destination.

Use the Multi-Car Family Advantage

Survey the vehicles available to you, and choose the one that's most fuel efficient. Why take the luxury car or heavyweight SUV on a quick trek to the supermarket when you could slip into your subcompact instead?

Another way to save fuel is to take the vehicle that's been driven most recently. As stated above, engines are grossly inefficient when cold. Start-ups are hard on the car and drastically cut into fuel mileage for the first few miles -- all the more so in cold weather. If you have at your disposal a vehicle whose engine isn't stone-cold, consider that one for your errand.

Investigate Alternative Routes

It's easy to get into a rut, taking the same route day after day, never pondering an alternative that might prove more economical -- and even more pleasant.

Experimenting pays. It doesn't hurt to study a map of the region you travel daily. Consider the number of stoplights along the way and the extent of traffic jams and slowdowns. Use your odometer to measure the distance covered by each route.

Sometimes, it's even wise to travel a little farther if that helps you avoid excess traffic. Whenever feasible, choose highway travel rather than city routes. Avoid routes that pass through school zones or follow school bus pickup points, which often require slowing to an uneconomical speed and perhaps stopping frequently.

Drive When Others Are Not Driving

Plan your time so you're traveling when most other people are not. Ask your employer about flexible work hours that keep you out of the morning and evening rush. Run errands at midday rather than 8:00 a.m. or 4:30 p.m.

Off-peak travel saves fuel and aggravation. Leave rush hours to those who have no choice in the matter.

Drive Where Others Are Not Driving

In the city, look for through streets with a minimum of stoplights. You might think you're saving time by darting down side streets and alleys in rush hour, but you're more likely wasting fuel from all the start-and-stop motion.

Tune into local radio and TV programs for up-to-the-minute reports on traffic conditions and accidents. Staying tuned is most vital in bad weather.

Consider Weather Conditions

Naturally, you can't change the weather, but the fact is that you'll burn considerably less fuel driving when the temperature is 70 degrees versus 20 degrees. In cold weather, try to travel in daylight rather than at night when it's chillier.

Wind also makes a big difference. A strong headwind, even a crosswind, cuts mileage drastically, as your engine fights its way forward. A tailwind can do the opposite.

Heavy rain and snow also hurt gas mileage, as well as making the travel experience less pleasant. So if you must drive in stormy weather, slow down when the wind is not at your back.

Dress Right

Running the heat burns more fuel. Keep that coat zipped and turn the heater blower down a notch or two.

In warm weather, dress lightly to avoid using the air conditioner until absolutely necessary. Even opening the windows creates aerodynamic drag, so proper dress can help you regulate your body temperature to stay comfortable and save fuel.

Explore Alternative Forms of Transportation

In a society that values private transportation, going without a car may seem like heresy. Yet surprising numbers of people do exactly that -- especially those who live in urban areas. Walking, after all, is excellent exercise and costs absolutely nothing.

Most cities have better bus service than many nonriders may realize. And in some urban areas, commuter rail service efficiently transports thousands of people to and from work each day. You'll give up some travel-time flexibility, but the duration of your commute may shrink, and you'll be free from the burden of locating and paying for in-town parking.

Lifelong rush-hour motorists may be amazed to discover how relaxing it can be to sit back on the bus or commuter train and read or doze. Train and bus schedules are readily available, usually online. If you can't see giving up the car commute entirely, what about taking mass transit once or twice per week?

Don't overlook the possibility of riding a bicycle instead of traveling by car. It's fine exercise. You won't have parking hassles. Many cities have bike lanes. And in rush-hour congestion, you may find that the maneuverability of a bike allows you to travel more quickly than by car. Approach this alternative with due caution, of course. The right bike, proper safety attire, and an alert mindset are essential.

A moped or motorcycle won't free you from all of the costs and burdens of motorized travel, but they afford many of the same advantages as a bicycle, with the obvious ability to go faster and cover longer distances. No matter how far you want to travel, the following tips can help you explore your alternative transportation options.

The Online Advantage

Finding the lowest gas prices in your area is just a mouse-click away. Several Web sites allow you to type in your zip code and view a roster of pump prices for your region. Just go to your search engine and type in "gas prices."

The Web also offers a universe of service options from the comfort of your home. Shop online instead of driving to the mall. Bank online instead of idling in a drive-up bank-window line. Conduct research via the Web instead of driving to the library. You can order videos, have digital photos developed, and even buy a car online.

Vacation Sensibly

Look into holiday spots where the need to drive after you arrive is minimal or nonexistent. Consider a self-contained resort where you'll enjoy a break from the stress of traffic congestion. Visit an exciting big city, where restaurants, shopping, entertainment, and museums are within walking distance.

If you prefer to take a driving vacation, do a little research on attractions close to home. You might have overlooked some great destinations.

Whether traveling near or far, start out when traffic is light. Plan meals and rest stops to coincide with peak traffic times in the area. There's no point in feeling like a commuter when you're on vacation.

Car Pool

Share the ride, share the costs. Talk with neighbors and coworkers about car-pool opportunities, even for just a couple days per week. You'll save on gas, parking, and wear and tear on your car since you will skip a day or two of stop-and-go driving.

You'll save time, too. Many highway systems around big cities have car-pool lanes, otherwise known as High Occupancy Vehicle (HOV) lanes, dedicated to vehicles carrying more than one occupant. While the regular lanes are clogged with crawling peak-travel-time traffic, the HOV lanes are often flowing freely. In rural areas, lots may be set aside as car-pool gathering points near a freeway on-ramp.

Sometimes, there's just no way around driving. On the next page, we'll give you some gas-saving tips for when you do need to get behind the wheel.

Gas-Saving Tips

Good drivers are smooth drivers, and smooth driving saves fuel. Even minor adjustments in how you drive can result in substantial savings in gas and money. You can stay in control by practicing the following guidelines.

Practice Mind Over MPG

We tend to allow our emotions to affect our driving. Whether you are elated or angry, calm down before getting behind the wheel.

Emotionally intense drivers are a lot more likely to engage in fuel-wasting (and dangerous) acts: gunning the engine, spinning the wheels, and worse.

Reconsider Remote Starters

Willing to sacrifice a few minutes of personal comfort to save some gas? Ignore that remote starter.

Remote ignition starters allow you to start your vehicle with the press of a keyfob button while still in the climate-controlled comfort of your home. The vehicle idles with the heater or air conditioner running, and you step into a warm or chilled interior. But an idling car that is running the air-conditioning is needlessly gulping down gas.

The alternative is to bring the vehicle's interior to your desired temperature as you drive, which takes only a few minutes and makes better use of the fuel you're burning.

Remote starters have been available through the aftermarket for years and recently have been offered as factory-installed options on some new cars. You'll have to judge for yourself whether a few minutes of personal discomfort balances the savings in fuel and the extra exhaust emissions associated with the use of a remote starter.

Fill the Tank Only When Needed

No point stopping for gas when there's still plenty in the tank. Let it get down to about one-quarter full. Extra stops waste time, and keeping more fuel than needed in the tank adds unwanted weight to your vehicle. A gallon of gas weighs roughly 6 pounds, and the more weight you haul around, the more fuel you'll burn.

Note that there are important exceptions to this rule. During extremely cold weather, keeping the tank near full minimizes the amount of condensation, or water, that can form in the tank. Excess condensation can promote fuel-line freeze and other problems.

Additional exceptions depend on your personal travel patterns. If you regularly drive long distances, at odd hours, in desolate conditions, or in hazardous weather, it's in your interest to keep a generous supply of gas in the tank. Plan for the unexpected.

Buy Gas on Cool Mornings

Liquids expand when warm, and that includes gasoline. So you actually get a bit more for the same amount of cash by buying gas when it's most dense, even though the pump shows the same total.

Gas Up Along the Way

As a rule, there's no point driving out of your way or making a special trip just to save a few cents per gallon. Make the service-station stop part of your regular route.

The exception is during periods of rapid price hikes. Then the difference could amount to more than pennies. So pay attention to current prices in your area, and take note of the stations that offer the most competitive prices.

Know Your Car's Correct Gasoline Octane Rating

The brand name of the fuel is of no importance to your engine. But the correct octane rating is vital.

Octane has nothing to do with a gasoline's quality. The octane figure indicates a fuel's resistance to "knocking." That's the metallic pinging sound you may sometimes hear when accelerating rapidly or lugging up a hill. Knock may be accompanied by run-on, or dieseling, in which your engine continues to turn over or sputter after you've switched off the ignition. Severe knocking or run-on, over an extended period, can damage engine parts.

There's no advantage in using a higher octane than is necessary to prevent knocking. In fact, today's cars have computerized controls designed to adjust ignition timing and other engine functions to keep knocking in check, so unless you hear something abnormal, you are probably using the right octane level for your car.Only a small percentage of vehicles require premium fuel. These automobiles are usually sport or luxury vehicles with high-performance engines, and those vehicles with turbo-charged or supercharged gasoline engines.

Regular-grade gas is usually rated at 87 octane, mid-grade at 89 octane, and premium at 91 or above. The higher the altitude above sea level, the lower the octane requirement. You'll see this reflected on the pump: at high altitudes, octane numbers are lower by one or two digits for the same grade of gas available at lower altitudes. Generally, the hotter the air temperature or the lower the humidity, the greater the octane requirement.

It's essential to consult your owner's manual to find out the proper octane level for your vehicle. (Some auto manufacturers also post the octane requirement on a sticker inside the fuel-filler door.)

Note that your owner's manual may list a particular octane level as "recommended" or "required." The "recommended" octane, usually midgrade or premium, is the one you should choose for "best" performance. The manual will state this. Your car will run fine if you choose not to follow that recommendation, and you'll be hard-pressed to notice the few horsepowers sacrificed to the lower octane. If a particular octane level is "required," however, use it.

As vehicles accumulate miles, their octane requirement can increase because of the buildup of combustion-chamber deposits. This continues until a stable level is reached, typically after about 15,000 miles. The stabilized octane requirement may be 3 to 6 numbers higher than when the car was new. Premium or midgrade fuel may be advisable to prevent knocking.

At the gas pump, a label on the pump shows the octane ratings available at that station. The higher the octane, the more you'll pay. Use the correct octane, and save.

Is there more you can do to conserve gas while you drive? Check the next page for additional tips on fuel-effecient driving.

Fuel-Efficient Driving

Driving with fuel economy in mind can help you conserve fuel and save money. Here are some steps you can take to ease up on your fuel consumption.

Ease Up on the Accelerator

Accelerate no more forcefully than needed to mesh smoothly into traffic. Racing up to cruising speed may make you feel like Jeff Gordon, but it'll quickly drain your wallet.

Fuel consumption is directly related to how hard the engine is working. Ask it to race away from a stop rather than accelerate sensibly, and you'll be visiting the gas station all too frequently. Guaranteed. Ask it to barge up a steep grade rather than feathering the throttle just enough to sustain momentum, and you'll watch the needle on your gas gauge move too quickly toward "E."

Even jabbing the accelerator during passing maneuvers or lane changes eats away at fuel economy. On the highway, zooming up to the traffic ahead, then having to hit your brakes, is a fuel-wasting exercise and a sure sign of an impatient driver. The best drivers are smooth and efficient in every move they make.

Lose Traction, Lose Fuel

Even if you're not trying to race away from a stop, you may find your tires slipping, especially on wet or gravel surfaces. Each time a tire slips, whatever the cause, you're losing gas mileage as well as endangering yourself. Take care when starting off on slippery or unpaved roads. Slow down on rough pavement.

Consider RPM and MPG

An engine's workload is determined by how fast the crankshaft is turning. The crankshaft transmits engine power to the transmission and then to the wheels, and crankshaft speed is measured in revolutions per minute, as indicated on a tachometer.

A manual transmission gives the driver full control over rpm because the driver can make the engine speed up or slow down via gear selection. The lower the gear, the higher the rpm. The higher the rpm, the more torque the engine is producing, and the more fuel it is using. Automatic transmissions take some of this control out of the driver's hands, but they, too, can be manipulated to maximize fuel efficiency.

Shift Smartly

With a manual gearbox, shift into the upper gears quickly. Optimal shift points vary, depending on the engine/gearing combination, but for best economy you might need to shift to second by about 15 mph, and reach top gear by the time you're traveling 30 to 35 mph.

Rule of thumb: If the engine is revving faster than necessary to sustain an even road speed, move to the next higher gear. Downshifting follows a similar standard. If the gas pedal has to stay close to the floor to maintain speed, you probably belong in the next lower gear. "Lugging" in too high a gear isn't good for the engine or your finances.

Take Advantage of the Upshift Light

If your manual-transmission car has an upshift indicator, use it as a guide. Using signals from the engine, transmission, and accelerator pedal, the indicator tells you exactly when to upshift to maintain greatest efficiency, and thus top economy.

When the engine speed is high compared to the position of the accelerator pedal, the shift indicator lamp signals that you can get the same performance with less fuel by shifting up without losing power.

Tests conducted by Saab and the EPA compared operation of cars that had an upshift indicator to those that did not. In the EPA city-driving test, use of the indicator yielded an average gas mileage improvement of more than 9 percent. Even without such an indicator, you should shift into a higher gear sooner than you normally would and use fifth gear as much as possible to stretch your fuel.

Watch the Tachometer

Because tachometers are no longer limited to performance models, more drivers than ever have a chance to pay attention to engine speed as well as road speed. This allows you to find the engine's most efficient rpm and stay close to that point whenever feasible. What speed is that?

The exact figure depends on the engine but is typically the speed at which it produces the greatest torque output. For economy's sake, it's generally wise to remain below 3,000 rpm most of the time and to shift into the next gear before the engine gets much beyond its optimum rpm level. Too low an engine speed does nothing for your finances, so running below 1,500 isn't ordinarily a good idea.

Skip an Occasional Gear

No rule says you have to use each gear of your manual transmission every time, going through a never-changing 1-2-3-4-5 sequence. Try going directly from first to third (skipping second); or go from second to fourth without using third. This technique is especially useful if heavy traffic has caused you to rev too high in the lower gear already, as when merging onto an expressway from the entry lane.

Get the Most from Your Automatic Transmission

An automatic transmission liberates you from shifting gears yourself, but nothing is free, and an engine must work a little harder and use a bit more gas to transmit power through an automatic transmission than a manual. For proof, look no further than EPA fuel economy estimates, which are invariably lower for an automatic transmission than for that same vehicle equipped with a manual transmission. Still, there are some things you can do to maximize fuel efficiency in an automatic-transmission vehicle.

During acceleration, listen as the engine note rises and then falls to get a sense of when the transmission is reaching the "top" of one gear ratio and changing down to the next lower ratio. Also, watch the needle on the tachometer climb up the rpm range and descend correspondingly. Remember, the higher the rpm, the more fuel you're burning.

Some automatic transmissions tend to stay in lower gears a little too long for peak economy. You can sometimes coax the transmission into shifting to high gear earlier than usual by letting up on the gas as you pass 30 mph or so. Then, once it's in top gear, continue to accelerate very gradually.

Watch That Little OD Light

Virtually all manual and automatic transmissions have an overdrive gear that can be employed to save fuel. It's usually the highest-numbered gear (or gears), and it lets the engine run at a slower speed (or lower rpm) while the car maintains the same road speed.

If you're looking to save gas, get into an overdrive gear as soon as possible and stay there until you need the extra power afforded by a lower gear.

With an automatic transmission, a lot of that decision making is out of your hands. Automatics tend to move to the highest gear on their own, precisely to save fuel; at cruising speeds, overdrive (OD) kicks in. But you can shift into and out of OD. On newer cars, it's usually done via a button on the shift lever. Typically, an "OD" light illuminates in the instrument panel when an automatic is shifted out of OD. If you have inadvertently shifted out of OD, press the button to get back in for optimal fuel economy.

Many modern automatic transmissions allow drivers to change gears manually by moving the shift lever through a separate gate. This doesn't duplicate the degree of gear control afforded by a manual transmission, but it will allow you to select a lower gear for more throttle response. Doing so increases engine rpm and burns more gas. For best fuel efficiency, shift into the highest gear whenever possible or simply shift into Drive and let the automatic do what it's designed to: Select the most economical gear at each step of the way.

Make Sure Nothing's Afoot

Don't drive with a foot resting on the brake pedal, however lightly. Even the slightest application of the brakes while moving will drag down fuel economy. It'll place an unnecessary burden on the engine and transmission. You'll wear out your brakes rapidly, as well.

Even when your car isn't moving, you should be thinking about ways to save gas. In our final section, we'll take a look at some ways to conserve fuel while your car is standing still.

Saving Gas While Standing Still

Even when your car is standing still, you can be saving gas. Here are some strategies.

Shift to Neutral When Stopped

If you're not moving but your engine is running, you're getting zero miles per gallon. Idling at a traffic light is a fuel-economy killer, as is waiting to clear a construction zone or sitting while a freight train crawls by. And there's a good reason our most frustrating traffic condition is called stop-and-go driving.

Notice that shifting your automatic or manual transmission into neutral calms down your engine note and drops the rpm. That saves gas. Shift into neutral even for a long traffic light.

Keeping an automatic transmission in Drive puts an extra load on it, which drains fuel. In neutral, it's resting -- or at least as close to rest as an automatic ever gets. This shift is even more important when the air conditioner is running, so the engine doesn't have to strain so hard while idling. A manual transmission should be shifted to neutral at every stop.

Shut off the Engine When Stopped

Even when stopped for a mile-long freight train, a lot of drivers keep their engines running. A minute of idling, however, consumes more gas than a restart.

So, whenever you expect to be stopped for a minute or more, shut off the ignition. No, not at every red light you come to, though some experts advise that even a 30-second stop is worth a shutdown. Use your judgment, but when standing in a bank drive-up line or at a fast-food drive-through, if it looks like a long wait without moving, turn off that engine.

Note that the new gas/electric hybrid vehicles automatically shut off the gas engine in most conditions if the vehicle is stopped for even a few seconds. They restart instantly as the gas pedal is applied. The engineers who designed those hybrids know the fuel-saving value of shutting off an engine.

Don't Race the Engine at Stoplights

It's hard to understand why people are inclined to tromp on the pedal -- sometimes every couple of seconds -- while waiting for a green light. What's to be gained, except drawing attention to yourself?

If you need to pump the pedal to keep the engine from dying, chances are fuel economy isn't your major worry -- in fact, you need to consult a mechanic.

On an Upgrade, Hang on With the Brake

When waiting at a stoplight or stop sign on an upward pavement, keep the car from drifting backward by pressing on the brake pedal in the normal manner. Don't use the clutch or automatic transmission to keep it from sliding back. This wastes fuel and puts a strain on the engine.

Shut Down When You Leave the Car

If it's a good idea to shut off the engine even when stopped for a minute while you're still in the driver's seat, obviously it's essential to do so when you stop and leave your car for awhile. Don't leave the engine idle while making a phone call, hopping into a store, or dropping off the dry cleaning. Sure, that might keep the interior warm in winter or cool in summer, but the gasoline is just burning away, accomplishing no useful purpose -- to say nothing of the fact that an idling car is just begging for a thief to drive it off.

Park it Sooner

If you're a city dweller, you know that finding that perfect parking spot is nearly impossible. Why even try? Don't waste time and fuel cruising for an ideal spot that is steps away from your destination. Pick the one that comes along first, even if it means walking a few blocks. The exercise will do you good.

In the same vein, park so you don't have to move your vehicle a short time later. Don't leave it sitting on the street or in the driveway so that you have to move it into the garage. By that time, the engine has cooled down, and you're wasting gas to start the car while putting extra wear on its parts.

Don't Rev the Engine Before Shutting Off the Ignition

Many of us learned to do this on carburetor-equipped engines in the belief that stomping the gas pedal as we turned off the switch would "prime" the carb (put a jolt of gasoline in its bowl). Most of the time, it did little or no good even for a carbureted engine.

For today's fuel-injected engines, it's a complete waste of fuel. Not only that, but the final spurt of gasoline also winds up dumped on the cylinder walls where it can wash away the essential lubricant, paving the way for increased wear.

Driving economically requires a few simple changes for most drivers, but it can yield good results at the gas pump. Keep the fuel-saving tips from this article in mind whenever you're behind the wheel.

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