The best way to burn less fuel is to buy a car that gets better gas mileage. But our tests with a Honda Accord, Toyota RAV4, and other vehicles show there are ways to save at the pump without buying a new car.
Drive at a moderate speed
This is the biggest fact. You may have to be a little patient, but driving at 55 mph instead of 65 or 75 will save you money. When we drove the Accord at a steady 65 mph, the car’s fuel economy dropped from 49 mpg to 42 mpg compared to 55 mph. Speeding up to 75 mph cost the car another 5 mpg. One reason is that aerodynamic drag increases exponentially the faster you drive; it simply takes more fuel to power the car through the air.
Using an SUV in the same test, our RAV4 dropped from 37 mpg to 33 mpg, then to 27 mpg at 75 mph.
Avoid hard acceleration and braking whenever possible. In our tests, frequent bursts of acceleration and braking reduced an older Toyota Camry’s mileage by 2 to 3 mpg. Once up to speed on the highway, maintain a steady pace in top gear. Smooth acceleration, cornering, and braking 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. So don’t carry things on top of your vehicle when you don’t have to. When we installed bikes on a rooftop carrier atop the Accord driving 65 mph, fuel economy dropped a whopping 35 percent, from 42 mpg to 27 mpg. Even the empty rack created enough drag to suck gas mileage down 5 mpg. Adding a wind deflector quieted things down but didn’t help the mileage: It dropped 2 more mpg to 35.
Don’t use premium fuel if you don’t have to
If your car specifies regular fuel, don’t buy premium under the mistaken belief that your engine will run better. The only difference you’ll see is about 20 cents more per gallon. Most cars are designed to run just fine on regular gasoline. Even many cars for which premium is recommended will run well on regular. We have found that the differences are imperceptible during normal driving. Check your owner’s manual to find out if your engine really requires premium or if you can run on other grades.
Minimize driving with a cold engine
Engines run most efficiently when they’re warm. And the most effective way to warm them up is to drive! The effects vary. But as an example, driving our city mpg test several times with a cold engine consumed an extra 4 mpg versus driving it as the engine warmed up. Engines also produce more pollution and wear faster when they’re cold. When possible, combine several short trips into one so that the engine stays warm.
Under-inflated tires hurt mpg
A midsized sedan did lose 1.3 mpg on the highway when the tires were under-inflated by 10 psi. That’s a sizeable drop in pressure for a modest drop in mpg. More important, though, under-inflated tires compromise handling and braking. Plus, they wear faster and run much hotter, which can lead to tire failure. For safety’s sake, check tire pressure at least once a month. The owner’s manual explains how to do it.
Lower rolling resistance tires save gas
A tire’s rolling resistance can add or detract another 1 or 2 mpg. But worn tires generally get better mileage than new ones with more tread. So even if you buy new low-rolling resistance tires, you’re unlikely to see any gain until you wear them down. Some high mpg tires also had good grip and did well in our tests, and they usually don’t cost more, so there’s no reason to shy away from models that did well in our Ratings. Look for high-rated tires with low rolling resistance. They could save you more than $100 a year in fuel.
Replace your air filter
Our tests show that driving with a dirty air filter no longer has any impact on fuel economy, as it did with older engines. 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 causes the engine to automatically reduce the amount of fuel being used. Fuel economy didn’t change, but the Camry accelerated much more slowly with a dirty filter.
A common tip is to buy gasoline in the morning, when the air is cool, rather than in the heat of the day. The theory is that the cooler gasoline will be denser, so you will get more for your money. But the temperature of the gasoline coming out of the fuel nozzle changes very little, if at all, during any 24-hour stretch. Any extra gas you get will be negligible.
Tailgates and tonneau covers
We tested a 2013 Ram V8 on the highway at 65 mph with the tailgate up, tailgate down, and with a factory soft tonneau cover. The tests were performed following our usual procedure for testing highway fuel economy, including making runs in both directions. We found that adding a tonneau cover or lowering the tailgate hurt fuel economy, rather than helped it.
With the tailgate up and no tonneau, we got 22.3 mpg. Dropping the tailgate decreased efficiency to 21.5 mpg. That 4-percent difference means that driving the Ram all year exclusively on the highway could cost the owner an extra 20 gallons of gasoline. (In reality, this big workhorse is likely to see a mix of driving and a variety of chores, limiting the potential penalty.) We found that covering the bed with a soft tonneau cover was even more detrimental, dropping fuel economy to 21.4 mpg.