Tips and Myths on Saving Gas

Q. Thanks for the information about wasting gas while idling the car. What else really saves fuel, and what are just hyped myths?

A. The best way to cut fuel costs, of course, is to drive a car that gets good mileage. That said, the easiest way to cut gas costs for any car is to maintain a highway speed of 55 mph. For each 10 mph over that, aerodynamic drag reduces fuel efficiency by around 5 miles per gallon (mpg), according to tests by Consumer Reports on a Toyota Camry.

Other fuel-saving tips:

• Pay attention to maintenance. Fixing a faulty oxygen sensor, for example, can improve your mileage as much as 40 percent. An improperly tuned car reduces mileage by about 4 percent, according to government tests.
• Accelerating and braking too fast reduce fuel efficiency by about 3 mpg, according to the Consumer Reports tests.
• Having tires that are under-inflated by about 10 pounds per square inch decreases fuel efficiency by about 1.5 mpg, according to Consumer Reports.

• Using the wrong weight of motor oil can reduce efficiency by about 2 percent, so check your owner’s manual. In addition to the correct weight, use types labeled “energy conserving” that contain friction-reducing additives.

But some commonly dispensed advice is actually of little help:

• Buying premium gas when your car requires only regular will not make a noticeable difference in your fuel efficiency.
• Dirty air filters often get blamed for reducing mileage, but Consumer Reports and FuelEconomy.gov say the impact is really minimal in newer cars (although a dirty air filter may cause more sluggish acceleration).
• Another debate: whether it’s better to cruise the highway with the air conditioner on and windows closed, or to keep the windows open and the AC off. There is no significant difference in fuel efficiency, according to tests.
• Another hyped tip is to buy fuel first thing in the morning. The idea is that when temperatures are cooler, the gasoline coming from the pump is denser, so you’ll get more for your money. But since the actual temperature of gas coming from the nozzle doesn’t change during the day, you’ll likely get no savings with an early fill-up.

Sid Kirchheimer writes about consumer and health issues.