Busted: 7 Things That Won’t Improve Your Gas Mileage

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Here at GreenCarReports, we often remind you what you can do to improve the gas mileage of your car with articles devoted to tire maintenance, good driving practice and following service schedules.

According to Consumer Reports however, there are just as many things that are rumored to improve your gas mileage that just don’t work on today’s modern cars.

Some, it has proven, including preferring air conditioning over open windows and choosing tires with low rolling resistance, don’t affect your gas mileage as much as you’d think.

Here are just seven of the mpg myths busted by the folks over at Consumer Reports. Read them, and let us know what you think. 

Cheap Gas Stations Give Cheap Gas

For years, there’s been a common belief among drivers that gas purchased at independent gas stations isn’t the same quality as gas purchased from name-brand gas stations.  

We’ve even heard rumors in the past that say some gas stations dilute cheap gas with small amounts of water, affecting power and engine efficiency.

Both, Consumer Reports says, are not true. 

In reality, all gas stations are tied by tight laws governing the storage and pumping of gasoline, while independent and no-name gas stations usually buy gasoline from the well-known oil companies anyway. 

The only difference? Cheaper gasoline sometimes omits the additives designed to clean older engines. With today’s modern fuel-injection systems however, that shouldn’t make much difference. 

Gas prices, San Francisco, CA

Gas prices, San Francisco, CA

Enlarge Photo

Premium gives better gas mileage

Because premium gas has a higher octane rating than midgrade or regular gas, it produces a little more power when burnt.

Designed for performance cars with large, powerful engines, premium also helps minimize the risk of preignition inside highly-stressed, hot engine cylinders. 

On a track, the extra boost given by premium can mean a few tenths of a second difference on a lap time. 

In the real world, it barely affects performance, or fuel economy. 

Consumer Reports advises that premium should only really be used in your car if your owner’s manual mandates it. In our experience, only a handful of everyday cars are tuned to run better on premium. 

Open windows kill fuel economy

Windows or Air Conditioning? 

It’s a common misconception that winding down windows on your car to provide ventilation creates so much extra drag that your gas mileage falls further than it would if you use the on-board air conditioning. 

Not so, says Consumer Reports. Under lab conditions, it tested a Honda Accord along a test track at 65 mph.  Using the air conditioning to keep the car cool impacted gas mileage by a shocking 3mpg. 

Keeping the windows open on the other hand, affected gas mileage so little that it was impossible to measure. 

2011 Nissan LEAF prototype

2011 Nissan LEAF prototype

Enlarge Photo

Low rolling resistance tires are always best

While tires specially designed to lower rolling resistance can save you a few mpg if properly inflated and maintained, Consumer Reports advises that better tire maintenance and driver habits can easily make up the difference between an energy saving tire and a regular tire. 

As it points out, lower rolling resistance tires often perform less well in wet and icy conditions than regular tires, raising your risk of accidents. 

The solution, it says, is to look for a good all-round tire that combines good economy, good tire life and good grip.

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Comments (13)
  1. The AC information is interesting. I had heard that at low speed, windows were better and at high speed AC was better. Perhaps that is not true.

    For the cold gasoline issue... One thing that can happen on a hot summer day is that the fuel truck can be hot, fill the underground storage tank with hot fuel, then when you pump it, you overpay. This would not happen if we purchased by the pound rather than by the gallon.

  2. I'm toying with the idea of taking off the factory fit low rolling resistance tyres on my Renault Fluence ZE. The grip is shocking and I'm pretty sure the tyres are to blame. Pulling away without activating the traction control is a very delicate operation.

    And in the end I don't care if I use 17kWh per 100km or 17.2kWh. It's really not a big deal.

  3. I have some serious doubt about the windows vs. A/C study. CR has known to do some "fishy" studies in the past. The article said "Lab condition". What does that mean? On a roller dyno? Hybrids cars and EVs will definitely suffer with windows down at 65mph...

  4. You seem to be a frequent contributor of illogical speculation with no evidence to back up your claims. Your post above is another example. I suggest you think and verify before posting such crap.

    CR is an non-profit organization that accepts no funds from anyone including auto, oil, and refrigerant companies. Why would CR conduct any "fishy" studies and what examples do you have? CR is an excellent, unbiased research organization that produces sound results. Are they perfect? No, but they are solidly straightforward at what they do.

    If you had the gumption to actually read and think before spewing your thoughts you would note that the article above states that CR drove the Accord around their test track. Not on a dyno dunder head.

  5. @Erik: Just a cautionary note about language. The basic content--an informed critique of another commenter's post--is fine, but please mind your language.

    FYI, our spam filter flags you for words like "cr*p" (although not "dunderhead"), so please try to use other words. Thank you in advance.

  6. Words like cr*p are flagged? Are we 5?

  7. Your kidding, right? Dunderhead? How 'bout fool or idiot? Is that ok teacher? You are being ridiculous!

  8. Write to me personally or have your management contact me. You are waaay out of line with your note above....dunderhead.

  9. CR only tested a current generation Accord. Does this mean that all vehicles new and used suffer no mpg decrease with the windows down? No. I'd like CR to test the Accord for a longer distance as well other types of vehicles like a full size pick up, small hatchback, and mid size SUV too. And were the windows just down a few inches, were they half way down, all the way down, just the front two windows or all four? We don't know. Perhaps the wind differences are significant at the CR test track versus the open highway...so why not perform the test in real world conditions? I'm a little surprised that CR didn't tell us the criteria they used for "windows down." They should have....

  10. As for mpg from different fuels, premium or octanes: Use 100% pure(ethanol-free) gasoline. With accurate records, switching our cars to 100% pure gasoline, our 3 cars' mpg increased 8.5%, 7-8%, & 5%. Also, all engines are smoother, quieter & have more power, such that less downshifting is needed to ascend hills. Gasoline engines were designed to get their best mpg using 100% pure gasoline, not 10% ethanol blends(duh).

  11. 10% Ethanol will reduce your mileage by at least 3-5% since it has lower energy content.

  12. Nikki you did not mention the best ones: Fuel line magnets, tornado vortex generators, brown gas/hydrogen/HHO kits, mythical 100MPG carburators etc.

  13. I strongly disagree with the opinion on dirty air filters. My own experience has been that they affect both performance and fuel economy. I have noticed this on every car I've ever owned, including fuel injected, electronically-controlled engines. I just don't buy that one.

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