6 myths about saving on gas

As gas prices continue to soar across the country, many people are desperate for ways to save money on gas, but some popular ways of purportedly improving your car's fuel efficiency do more harm than good.
As gas prices continue to soar, many Canadians are searching for ways to increase the fuel economy of their cars. (Nathan Denette/Canadian Press)

As fuel prices continue to rise across the country, many people are desperate for ways to save money on gas. Over the years, motorists, mechanics and other car enthusiasts have come up with a number of methods of purportedly improving a car's fuel efficiency.

Here is the truth behind some of the most popular gas-saving myths:

Over-inflate your tires

Myth: Keeping tires inflated above their recommended pressure will help maintain a car's optimum fuel consumption.

Fact: Every five pounds per square inch (psi) of tire pressure you lose can translate into a two per cent loss of gas mileage. You can usually find your recommended pressure on the inside of the driver's side door.

You may think that over-inflating your tires would save money on gas. In 2009, Popular Mechanics tested this premise by over-inflating the tires on a Honda Fit to 45 psi — 13 psi above the recommended pressure but five psi below the maximum.

On a drive from Los Angeles to Phoenix, the magazine's writers recorded a fuel consumption of 42.19 miles per gallon (5.575 litres per 100 kilometres). On the return trip, they inflated the tires to the recommended 32 psi, and the car's fuel consumption was nearly identical, at 42.14 mpg (5.581 L/100 km).

They noted that driving with over-inflated tires greatly reduced the car's handling and made for a bumpier ride. If you over-inflate your tires too much, i.e. above the maximum, there is also the risk a tire could burst.

Fill your tires with nitrogen

Myth: Some car dealerships and garages have begun offering to fill a customer's tires with nitrogen gas instead of compressed air, with promises of increased performance and better fuel consumption.

Fact: According to, this practice amounts to no more than a way for the garages to make a quick buck — the difference is negligible.

5 ways to really save on gas

  • Don't speed. Jim Davidson, author of 75 Ways to Save Gas, says drivers should keep their speed between 50 and 80 km/h whenever possible and avoid driving faster than 93 km/h. "Every 10 km over 93 km/h is 10 per cent fuel loss," he said.
  • Drive safely. Aggressive drivers tend to use more gas because they usually need to slow down and speed up repeatedly in order to avoid catastrophe.
  • Monitor your tire pressure. Davidson suggests driving with a tire pressure gauge and checking pressure regularly. Under-inflated tires cause drivers to use more gas because the car becomes difficult to accelerate.
  • Service your car regularly.
  • Change your tires seasonally. The increased grip and traction on winter tires means cars use more gas, so it's best to switch to a different set of tires in the warmer months. All-season tires tend not to work as well in snowy conditions.

Nitrogen gas is used in commercial aircraft, high-performance race cars and some long-haul trucks because it is a pure gas, unlike air, which contains several different gases. That enables engineers to more precisely predict how it will react at high temperatures, which cause the gas inside the tires to expand and inflate the tires.

It's especially useful for airplanes because their tires undergo a lot of stress and temperature variations: from warm temperatures at take-off to freezing temperatures during flight and back to average temperatures prior to landing. When a plane lands, friction causes intense heat, which will affect each tire's pressure.

Filling your tires with nitrogen instead of compressed air has no bearing on fuel consumption, as long as they are properly inflated.

Get gas in the morning

Myth: Many fluids, including gasoline, are denser at colder temperatures. Therefore, it would lead one to reason that filling up your car with gas in the wee hours of the morning, when it's cold, would give you more bang for your fuel buck. 

Fact: The reality is service stations store their gasoline in underground fuel tanks, where the temperature is nearly constant all day and night. You may end up saving a penny or a fraction thereof by filing up in the morning, but any savings would be negligible.

Open windows cause drag

Myth: The argument goes that even though running your car's air conditioning will reduce your gas mileage, it makes more sense to run the A/C on the highway because of the drag caused by opening your car's windows. 

Fact: In 2011, Consumer Reports tested this theory and drove a Honda Accord on the highway at a speed of 105 km/h with the air conditioning on and reported that gas mileage was reduced. Driving the same car at the same speed but with no air conditioning and the windows down yielded no noticeable change in gas mileage.

Shift into neutral when driving downhill

Myth: The (misguided) idea behind this popular myth is that by shifting to neutral when driving downhill, you cut off the fuel supply to the car engine and it stops burning gas.

Fact: Modern fuel-injected cars continue to burn fuel when you take your foot off the gas pedal as only the fuel-delivery system shuts down. That's why idling your car laps up so much gas. Coasting in neutral down a hill, therefore, does not increase fuel economy because the car still uses gas. A better idea would be to coast in drive because constant shifting between gears, with an automatic transmission, could cause transmission shock.

Change your air filter regularly

Myth: The air filter in your car is designed to keep dust and dirt out of your motor in order to maintain performance, so keeping the filter clean will keep your motor running efficiently, right? Wrong.

Fact: Many of us change our air filters on the recommendation of a mechanic, usually when we get an oil change. However, modern air filters are actually designed to work more efficiently when dirty, using the dust and dirt as an added filter layer. A 2009 study conducted by the U.S. Department of Energy found that a dirty air filter had no effect on gas mileage in modern cars using fuel-injection technology. The study does say a dirty filter may result in acceleration difficulty and therefore shouldn't be left in place indefinitely. An air filter should be changed after about 48,000 km.