Check out these gas-saving tips, myths

As the summer travel season rolls in, prices at the gas pump are usually going in the wrong direction for our wallets, notes Consumer Reports. That’s when drivers become more concerned about how to squeeze the most miles from their fuel dollars and keep their cars running their best.

Here are some common questions that Consumer Reports’ auto experts often get asked about gas mileage and related topics:

What’s the best way to cut fuel costs? Slow down. In tests, Consumer Reports found that driving faster on the highway can take a bite out of your car’s fuel efficiency. Testers measured gas mileage while driving at a steady 55, 65 and 75 miles per hour in a Honda Accord, Toyota RAV4 and three versions of a Ford Fusion, including a hybrid. The drop in fuel economy while going from 55 to 65 ranged from 4 to 8 miles per gallon. Upping the speed from 65 to 75 cut it 5 to 7 mpg more. Overall, speeding up from 55 mph to 75 is like moving from a compact car to a large SUV.

What if I need to carry stuff on my car’s roof? Carrying things on the roof increases aerodynamic drag, which hurts fuel economy. When Consumer Reports tested a 2013 Honda Accord at a steady 65 mph, it got 42 mpg with nothing on the roof. Adding even an empty bike rack dropped the mileage by 5 mpg, to 37. A wind deflector reduced the wind noise but cut gas mileage to 35 mpg. And with two bikes on the rack, gas mileage dropped to 27 mpg, a whopping 15-mpg difference overall.

Does running the air conditioner hurt fuel economy compared with opening the windows? It depends on how hard the air-conditioning system has to work. When Consumer Reports measured the fuel-economy difference in a 2008 Ford Focus, Honda Accord and Subaru Forester, testers found that fuel use with the A/C running went up with higher outside temperatures. At 55 degrees, there were negligible differences. But when testers measured again on days when the temperature was in the low 70s and high 80s, they got fewer miles per gallon with the A/C on. In general, expect 1 to 4 mpg fewer with air conditioning.

How far can I go when my 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 miles or so at a moderate speed. To maximize those last couple of gallons, Consumer Reports suggests slowing down and maintaining a steady pace.

Can I improve gas mileage by installing a special air filter? With modern cars, changing your air filter probably won’t improve your fuel economy. When Consumer Reports tested a car to see whether a dirty air filter hurt its gas mileage because of reduced air intake, it 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-to-fuel ratio. Testers expect similar results from any air-filter change.

Can running on empty hurt my engine? Some people think that can draw in debris from the bottom of the fuel tank, but it’s not a big concern. That’s because the fuel pump always pulls in gas from the bottom of the tank, even when it’s full. So if there is a debris problem, you’ll probably know about it long before the fuel level gets low. These days, there’s usually a fuel filter in the gas tank as well as one nearer the engine, so debris is unlikely to get through to your engine. If your tank contains junk, though, you might have to change the filters more frequently.

2014 Consumers Union Inc.