Don’t top off your tank: Debunking myths about fuel efficiency as gas prices skyrocket

Vehicles line up for fuel at a Domo gas station in central Edmonton on March 19, 2026.

Don’t top off your tank. Roll your windows down. Or don’t.

There are quite a few tips and tricks out on the internet about how to increase your car’s fuel efficiency, especially with prices at the pumps keeping Edmontonians – and Canadians in general – wary of their gas usage.

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One Northern Alberta Institute of Technology (NAIT) auto technician says making the most of your gas tank starts with good habits in two major categories: good general maintenance and tire pressure.

“Keeping your vehicle up to maintenance has a huge impact on your fuel mileage and your fuel efficiency in general,” Dustin Gagnon told CTV News Edmonton.

“That includes things like changing your filters, changing your oil … air filters. If you have a plugged air filter, you’re going to be causing the vehicle to run extremely inefficiently, because it can’t properly measure the amount of air coming in, so it can’t properly put the right amount of fuel in to match it.”

Tire pressure, he went on to explain, affects drag: the more tire in contact with the road, the more you’re dragging your vehicle.

“It doesn’t seem like it would be that big of an impact, but even a couple of PSI (pounds per square inch) can cause a pretty noticeable difference in your fuel mileage.”

Maintenance costs incurred, on top of rising gas prices, can feel a little daunting. But Gagnon says paying now to keep your car in good working condition means offsetting costly fixes down the metaphorical road.

In the meantime, he’s debunked a couple of myths about keeping your car from running on fumes.

Braking, speed and cruise control

A lot of busy commuter driving in Edmonton happens on arterial roads pocked with stop signs and lights that may not be working in your car’s favour.

Braking hard and often, Gagnon said, is wasting energy your car works hard to build up.

“If you think about how brakes work, basically, you spend a lot of fuel and a lot of energy to get up to speed, and then when you step on the brakes, you’re turning all that fuel that you just burned into heat that just goes off into the air,” he explained.

“If you’re spending a lot of time accelerating hard and then braking hard, all you’re doing is turning all that extra gas that you don’t want to spend money on into heat.”

He recommends being lighter on both the accelerator and the brakes to compensate for the on-and-off nature of city driving.

“Change your driving habits a little bit. It can definitely improve your mileage substantially.”

In a similar vein, cruise control on Anthony Henday Drive trips or otherwise can be a great way to save fuel efficiency as it stabilizes the amount of force on the accelerator.

“All highway speeds are generally pretty much the same, unless you’re doing something crazy like 150-160 km/hr, when you start to see more wind resistance,” he said.

Air conditioning vs. windows down

You might’ve heard an idea floating around that there’s a correct time and speed to be running your air conditioning vs. rolling the windows down. Gagnon says there’s some truth to which one matters – but it comes down to doing what your vehicle was designed to do.

“If you’re running your air conditioning, it is going to take more fuel to keep it operating. However, rolling your windows down is a much, much bigger drain than turning the A.C. on,” he said.

“Modern A.C. systems are very efficient. Driving your vehicle around with the windows down is providing a huge amount of extra drag, which is always, in my opinion, going to increase the fuel consumption more than running the air conditioner would at any speed.”

Don’t top off your tank at the gas station

When the fuel pump clicks after your tank is full, it could be muscle memory to give it a couple taps to fill it up. Gagnon says that’s counterintuitive.

“Fuel systems are sealed. Because we want to keep all the fuel in the tank, there needs to still be a bit of room for expansion, because fuel does expand and contract when it gets hot and cold outside,” he explained.

“If you keep topping off your tank, what happens is there are emission components that trap the fuel vapour from escaping to the atmosphere in your fuel system. If you keep clicking off and pumping as much gas as you possibly can into there, that fuel has nowhere to expand to.”

That extra fuel could expand instead into emission control devices that would damage your car in the long run.

That being said, fill up whenever you want – there’s a balance

Keeping your car going until the little empty light comes on isn’t necessarily recommended, but being overly cautious of how full your tank is is also a concern of the past, Gagnon says.

“The old adage of keeping your tank topped up all the time was really when fuel systems weren’t very well sealed, so you could get evaporation and you would lose some fuel just to the atmosphere. But in modern vehicles, that’s not the case,” he said.

“The bigger issue is, if you’re always running your fuel tank empty, is that the fuel in the tank is actually what cools off the pump and the fuel system … you can cause damage to the fuel pump, and that would be more expensive than fuel, that’s for sure.”