6 Gas Mileage Myths

Apr 13, 2012 by

gas price signA recent CBC online article exploded several myths about improving your car’s fuel economy. How many of these do you think of as conventional wisdom?

Over-inflate Your Tires

On the theory that less rubber in contact with the pavement means better gas mileage, many drivers over-inflate their tires. But in 2009 Popular Mechanics demonstrated that over-inflating tires has no affect on mileage, and will make a car handle poorly and cause a bumpier ride.

Popular Mechanics drove a car between Los Angeles and Phoenix—one way with the tires properly inflated, and returning with the tire pressure 13 psi above the recommendation (but 5 psi below the maximum). The testers recorded a negligible difference in fuel economy.

On a related note, for every 5 psi below the recommended inflation pressure, a vehicle’s gas mileage decreases up to two percent.

Fill Your Tires With Nitrogen

Wheels.ca tested this practice and found an immaterial impact on gas mileage, but not on drivers’ wallets.

Fill Your Tank in the Morning

The density—mass per unit volume—of all liquids increases as temperature decreases. So some conclude that a gallon of morning, and presumably colder, gasoline has a greater mass than a gallon of late afternoon gasoline. But since gasoline is stored in underground tanks, its temperature, and so its density, changes very little during the course of a day.

Opening Windows Cuts Mileage More Than A/C

Consumer Reports tested this accepted wisdom in 2011. Its experimenters drove a Honda Accord on the highway with the air conditioning on and logged a 3 mpg fuel economy hit. They then drove the car at the same speed with the A/C off but the windows down. The fuel economy matched their experience with the A/C on.

Glide Downhill in Neutral

Modern, fuel-injected cars still burn fuel when your foot is off the gas pedal. Moreover, you risk transmission shock by frequently shifting between gears in a car with automatic transmission.

Change the Air Filter Regularly

A 2009 study by the U.S. Department of Energy found no affect on gas mileage from a dirty air filter in modern, fuel-injected cars.

I tend to focus on one foolproof method for controlling gasoline expense: Drive fewer miles.

What’s your favorite proven strategy for stretching costly gasoline?

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