DRIVING TIPS THAT MAKE THE MOST DIFFERENCEMinimize driving with a cold engine. Engines run most efficiently when they're warm. In our city-driving tests, making multiple short trips and starting the engine from cold reduced fuel economy for both the sedan and SUV. Engines also produce more pollution and wear faster when they're cold. To minimize cold-engine driving, avoid making a lot of separate short trips with a cold engine. Instead, combine short trips into one so that the engine stays warm.Drive smoothly. Avoid hard acceleration and braking whenever possible. In our tests, frequent bursts of acceleration and braking reduced the Camry's mileage by 2 to 3 mpg and the Mountaineer's by about 1 mpg. The harder you accelerate, the more fuel you use. Unnecessarily hard braking wastes the fuel you use to get up to speed. Drive smoothly and anticipate the movement of traffic. Use your brakes as little as possible, since every time you hit the brakes you are wasting fuel. Once up to speed on the highway, maintain a steady pace in top gear. Smooth acceleration, cornering, and braking not only save fuel but also extend the life of the engine, transmission, brakes, and tires.Reduce unnecessary drag. At highway speeds, more than 50 percent of engine power goes to overcoming aerodynamic drag. Don't add to that drag by carrying things on top of your vehicle when you don't have to. We installed a large Thule Cascade 1700 car-top carrier on our sedan and SUV. Keep in mind, however, that the effect varies, depending on the model. Driving with the carrier cut 6 mpg from the normally aerodynamic Camry, dropping it from 35 mpg to 29. It only reduced the boxier Mountaineer from 21 mpg to 20. Even driving with empty racks on the car reduces its fuel economy.Slow down. Aerodynamic drag exponentially increases on the highway the faster you drive. We tested our vehicles' fuel economy at 55, 65, and 75 mph. Driving at 75 mph instead of 65 reduced the Camry's gas mileage from 35 mpg to 30. For the Mountaineer, fuel economy fell from 21 mpg to 18. Slowing down to 55 mph improved the gas mileage by similar margins: The Camry improved to 40 mpg and the Mountaineer to 24 mpg.IMPORTANT DRIVING TIPS THAT HAVE LITTLE EFFECT ON FUEL ECONOMYKeep tires inflated. Our tests show that driving on moderately underinflated tires is more of a safety concern than a fuel-economy issue. We set the pressure in all four tires to 10 psi below that recommended by the automaker. This reduced highway fuel economy slightly, by about 1 mpg for the Camry and by a much smaller margin for the Mountaineer. But more importantly, underinflated tires provide much less grip for turning and stopping and run much hotter. Overheated tires wear faster and can lead to a blowout. Check the pressure of your vehicle's tires at least once a month, when the tires are cold. Also check the tires before and after long road trips. The recommended tire pressure is found on a label inside the car—usually in a doorjamb, inside the glove-box lid, or inside the fuel-filler lid.Keep your air filter clean. According to our tests, driving with a dirty air filter in modern engines doesn't have a significant impact on fuel economy, as it did with older engines. While fuel economy didn't change, however, power output did. Both cars accelerated much more slowly with a dirty air cleaner. We drove both vehicles with their air cleaners restricted and found little difference in gas mileage with either engine. That's because modern engines use computers to precisely control the air/fuel ratio, depending on the amount of air coming in through the filter. Reducing airflow, therefore, caused the engines to automatically reduce the amount of fuel being usedUSING AIR CONDITIONING VS. OPENING THE WINDOWSAir conditioning places more load on the engine, which can affect fuel economy. But some auto journalists say that opening the windows at highway speeds can affect fuel economy even more by disrupting the vehicle's aerodynamics. In our tests we found that neither makes enough of a difference in fuel economy to worry about. Using air conditioning while driving at 65 mph reduced gas mileage in both vehicles by about 1 mpg-it might make more of a difference if you drive faster. The effect of opening the windows at 65 mph was not even measurable. Because air conditioning can help keep you comfortable and alert and because most modern cars use it to keep windows defrosted, we suggest that the small trade-off in fuel economy for increased safety is worthwhile.DON'T USE PREMIUM FUEL UNNECESSARILYIf your car specifies regular fuel, don't buy premium under the mistaken belief that your engine will run better. Most cars are designed to run just fine on regular gasoline. Furthermore, many cars that recommend premium fuel also run well on regular. Check your owner's manual to find out if your engine is designed to handle either grade. Think twice about using the more expensive gas even if your owner's manual suggests "for optimum performance use premium." We have found that the differences aren't perceivable during normal driving. However, if your car "pings" or knocks with lower grade fuel, buy premium.PAYING FOR PREMIUM GAS CAN BE A WASTE OF MONEYMany people use premium gasoline in the belief that it's better for engines than regular. That can be a costly mistake, especially during times of high fuel prices. Most cars are designed to run just fine on regular gasoline. Octane grades don't represent a "good, better, best" choice; they simply measure the resistance of fuel to knocking or pinging, a condition in which gasoline burns uncontrollably in the engine's combustion chambers. Knocking and pinging can damage an engine.While high-octane formulations resist knocking better than lower octanes, most engines are designed to take regular gas, which has an octane rating of about 87. Engines requiring premium gas are typically the more powerful ones found in sports and luxury vehicles. Those engines use a very high compression ratio, making them more vulnerable to knocking, so recommended fuels have octane ratings of 91 or higher. Using premium gas in an engine designed to run on regular doesn't improve performance. We have found that the differences aren't perceivable during normal driving.Some engines for which premium gasoline is recommended can run on regular without problems. That's because the engine's knock-sensor system detects the presence of uncontrolled burning in the chambers. When it does, the engine's computer-control system retards engine timing, eliminating the knock but slightly reducing power. If you don't mind giving up some performance, you can run these engines on less-expensive regular gasoline. To check whether your engine is capable of running on regular gas, read your owner's manual or ask your dealership's service department. However, if your car "pings" or knocks with lower grade fuel, buy premium.
