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?

  • http://frugalportland.com/ Frugal Portland

    my car gets amazing gas mileage if I’m using it primarily on the freeway. Not that I’m thrilled to always drive 100 miles, but it is nice to see those numbers!

    • http://mymoneycounselor.com/ Kurt Fischer

      Do you have a hybrid?

      • http://frugalportland.com/ Frugal Portland

        (just saw this) no, no hybrid. I couldn’t make that math work — the hybrid was $8K more than my car.

  • http://twitter.com/seedebtrun See Debt Run

    i have heard a few of these tips.. and questioned them at the time. notably, the windows down and the cruising downhill in neutral.. carpooling, combining trips, lightening your load (emptying your trunk) when you do drive, and asking your boss if you can work from home 1-2 times p/week is how i got my fuel costs down.

    • http://mymoneycounselor.com/ Kurt Fischer

      Working from home–that’s long overdue. Besides saving gas, just think how much society would save on building highways and time lost sitting in traffic if commuting were cut even 20%.

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  • thisthatand themba

    Not driving!  I love those people on the highways I think they are called hyper-milers or something like that.  They stay right inside the drag behind the 18 wheelers so that their car doesn’t catch all the wind and they get ridiculous mileage.   I don’t really pay too much attention to it as I drive about 2 miles to work.  My truck is a gas hog though when we take trips.

  • http://thecollegeinvestor.com/ The College Investor

    I thought you filled your tires with Nitrogen because they would deflate/change pressure slower.  Since air molecules are smaller than nitrogen, they react differently to temp.  I didn’t think it had anything to do with mileage.

  • http://www.101centavos.com/ Andrew @ 101centavos

    Driving less…. now there’s a thought!  Just like our own energy conservation program at home… turn off the lights. :-)

  • http://www.goldenfinancialnuggets.com/ Rianka D.

    Two valuable lessons here – 1) I do not have to freeze my butt off in the morning to fill up my gas tank to think I am getting more gas and 2) when I am running low on gas on the interstate in the summer I no longer have to sweat and be anxious that I am going to run out of gas.  I can be cool with the a/c on and anxious. Haha. Thanks for the post! 

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