How to Get the Best Fuel Economy Now
Try our test-based tips to save at the pump, and see which myths we bust
How you drive can significantly affect your fuel economy. That’s the key finding of CR’s fuel-economy tests. Even when fuel prices are very low, you can still save serious money by making small changes to your driving style and habits.
CR has gathered its best test-based tips and techniques for getting the most gas mileage from your car to help ease the pain at the pump.
The FAQ below addresses common questions we receive and dispels some fuel-economy myths.
What's the Best Way to Cut Fuel Costs?
Slow down. In our tests we’ve found that driving faster on the highway can really take a bite out of a car’s fuel efficiency.
We measured gas mileage while driving at a steady 55, 65, and 75 mph in a Nissan Altima and Toyota RAV4. Reducing speed from 65 mph to 55 mph improved fuel economy by 6 mpg in the Altima and 8 mpg in the RAV4.
The penalty of cruising at 75 mph, rather than 65 mph, was almost 7 mpg in the Altima and 6 mpg in the RAV4.
These findings are similar to what we have recorded in the past, once again proving that higher speeds exact a toll in fuel consumption.
What's the Impact of Carrying Stuff on the Roof?
At highway speeds, more than 50 percent of engine power goes to overcoming aerodynamic drag. Don’t add to that by carrying unneeded things on the roof. We did fuel economy tests at highway speed on a Nissan Altima and Toyota RAV4 with a roof rack, tail-hitch rack, and a roof-top box.
Carrying two mountain bikes on the roof had the biggest impact. The Altima lost 13 mpg, going from 46 mpg down to 33. The RAV4 lost 7 mpg, dropping to 32 mpg from 39 mpg.
There’s even a loss when driving with the empty roof rack installed: The Altima dropped 5 mpg and the Toyota lost 2 mpg.
The Nissan lost 12 mpg with the bikes on the hitch-mounted rack, while the RAV4 was down only 5 mpg. The bikes stuck out to the sides of the sedan, which created extra drag. They were mostly hidden behind the wider, boxier RAV4’s bodywork.
The roof-top box resulted in a 9 mpg decrease for the Altima, and a 5 mpg drop for the RAV4.
Overall, the aerodynamic drag doesn’t hurt the more boxy RAV4 as much as the sleeker Altima.
Going across town, this may not be a concern. But on a multistate family road trip, a carrier or rack on the roof would have a real impact on fuel costs. And it could create some annoying wind noise.
Use AC or Open Windows?
The harder the AC system has to work, the worse the impact on fuel economy. When we measured the fuel-economy difference in a 2008 Ford Focus, Honda Accord, and Subaru Forester, we found that fuel use with the AC running went up with higher outside temperatures.
At 55° F, there were negligible differences. But when we measured again on days when the temperature was in the low 70s and high 80s, we got fewer miles per gallon with the AC on.
In general, expect a drop from 1 to 4 mpg with the air conditioning running. The effect of opening the windows at 65 mph was not measurable. In any case, the AC helps dehumidify the cabin, which can contribute to keeping the driver alert and safe. We think that’s a worthwhile trade-off.
How Far Can You Go When the Low-Fuel Warning Light Comes On?
There is no set rule, but most cars have a reserve of between 1 and 2 gallons of gas when the light goes on, or enough to travel about 40 to 50 miles or so at a moderate speed.
To maximize those last couple of gallons, we suggest slowing down and maintaining a steady pace. Because you never know what challenges life will serve up, including traffic, don’t rely on the light as your cue to fill up.
Can Running on Empty Hurt the Engine?
Some people think that running on empty can bring debris into the engine from the bottom of the fuel tank, but it’s not really a big concern.
The fuel pump always pulls gas in from the bottom of the tank, even when it’s full. If there were a debris problem, it would surface long before the fuel level gets low.
These days, there is usually only one fuel filter in the gas tank that is not serviceable without pulling the pump out. If there is junk in the tank, repair costs can be much higher. With the introduction of plastic fuel tanks, rust in the fuel tank is not a concern like with vehicles in the past.
Does a Dirty Air Filter Hurt Gas Mileage?
Changing the air filter probably won’t improve fuel economy with modern cars. When we tested a car to see whether a dirty air filter hurt its gas mileage because of reduced air intake, we found that the car’s acceleration was hurt but not its fuel economy.
The engine’s computer automatically compensated for the restricted airflow by reducing fuel use to maintain the right air-fuel ratio. We expect similar results after any air-filter change.
Should You Warm Up the Car Before Driving?
Nope. That adage held in the days of carburetors, but it isn’t the case with modern fuel-injected, electronically controlled drivetrains.
Engines are most efficient when they’re at regular operating temperature, and the fastest way to reach that point is to drive right after starting the car.
Should You Refuel When the Air Is Cool?
Any extra gas gained by refueling when temperatures are cooler will be negligible and will not make a practical difference. A common myth 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, providing more go for the money. But most stations store the gasoline underground, so its temperature changes very little, if at all, during a 24-hour stretch.
Do 'No Name' Gas Stations Offer Lower-Quality Fuel?
Independent stations usually buy their fuel from larger, name-brand oil companies, so it’s not much different from what is offered for a higher price down the road. Off-brand gasoline is sometimes formulated without additives designed to clean the engine, but your car should run fine on that gas.
Better-quality gas is considered “top tier,” and it is available from many brands, including some less popular ones.
Should You Switch to Low-Rolling-Resistance Tires?
The lower the tire’s rolling resistance, or road drag, the better the fuel economy will be. However, maintaining the proper tire pressure will optimize the rolling resistance and real-world performance for any tires—even the tires currently on a vehicle.
Some tires reduce resistance at the expense of wet-braking performance and tread life—a poor trade-off.
It’s better to look first for a tire that provides good all-around performance in important safety areas, such as braking, handling, and hydroplaning resistance. Then use its rolling resistance level as the tiebreaker.
Don’t replace your tires too early in an effort to chase the pennies that low-rolling-resistance tires may save in fuel. (See our complete tire buying guide and ratings.)
What Role Does Tire Pressure Play?
A midsized sedan lost 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 a car's handling and braking. Plus, under-inflated tires 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.