If you’ve ever driven your car or truck on a cold day, you’re probably already well familiar with the fuel economy hit that comes with the mercury dropping below zero. Even electric vehicles can’t escape the grasp of winter, losing range and even taking longer to charge. So why is your car less efficient when it’s cold out? And can you do anything to help stop it? Because the only thing worse than spending more on fuel is standing outside pumping it at 30 below.
We’ll start with the things you can’t change. Like the air. Colder air is denser. There are more particles of air and moisture in every cubic metre of it. You might not feel the difference when you’re walking, but the density rises by nearly 20 percent when the temperature goes from +25 to -25C. Natural Resources Canada says that the difference between winter and summer air alone increases highway fuel consumption by 1.3 percent. They also point out that it’s windier in the winter too, and driving into the wind uses even more fuel and electrons.
Gasoline changes from summer to winter. When it’s cold, gasoline doesn’t like to vaporize, which you need it to do in order to burn in your engine. So refiners change the mix to make it more volatile. That means your engine runs, but there’s less energy in that gas. About 2 percent less, which is why you might notice your fuel bill starting to increase in October even though it’s not freezing yet. Gasoline companies like to be ahead of the curve so you aren’t stranded.
Tire pressures change with the cold. If you had your winter tires installed before the thermometer dropped below 7°C, which tire makers recommend, then by the time it hits -20°C your tires would have lost around 7 psi. That negatively affects handling and braking, makes your car more susceptible to pot hole damage, and it uses more fuel or electricity to move the vehicle. Surprisingly, the winter tire itself may have less of an impact than you might expect. Tire manufacturers like Nokian say that winter tires actually have less rolling resistance than summers, not more.
Cold engines use more fuel. Even before you start moving, the computer is telling the injectors to put more fuel into the engine. It will keep the car at higher RPM for a short time as well. That’s to try and keep it running while cold and to warm up the engine (and more importantly the catalytic converter) more quickly. Once you start moving, the oil, transmission fluid, and other liquids in the engine are thicker. That means more friction until they warm up. If your car, truck, or SUV has transmission and oil temperature gauges you can see just how much longer it takes those fluids to reach operating temperatures.
Not so fast, electric cars. While EVs might not have to worry about winter gas and cold oil, they are still affected by air density and tire pressure. And batteries have their own cold-weather challenges. Lithium-ion batteries start to noticeably lose performance at around 5°C. If you’ve ever wondered why Pokemon GO! and Angry Birds drained your phone in a fraction of the normal time while you sat in the cold rink or while you walked around outside, that’s why. The fluid in the battery that lets it do those magic battery things gets thicker. And less effective.
That can cut range by 20 percent compared with the summer. But a cold battery has effects that go beyond just discharge. Since cold batteries don’t work, many EVs have a heating system to keep them from getting too cold. Which, of course, uses power and reduces range. At least if you aren’t plugged in. Which brings us to the next cause. Those cold batteries can’t discharge, but that means they don’t charge as well either. US Department of Energy research showed that at 25°C, a battery could charge to 80 percent capacity in 30 minutes. But at 0°C, a 30 minute charge would get 36 percent less energy into the battery. At very cold temperatures, the charging rate could be a third of the summertime rate.
Then there are the changing conditions. The things don’t happen all winter, but that you can’t really avoid. Like snow. Or slush. They drag your vehicle down, increase wheel slippage, and suck down fuel and electric range. The EPA shows that snow can impact consumption up to 35 percent. Running the rear defroster increases the electrical load on both types of cars, and using the front defroster normally means the air conditioning is on and that doesn’t help. Electric cars only have electric heat, which means running the seat and steering wheel heaters plus the cabin air heat can really dig into how much is left to get you where you want to go.
Now we get to one of the big things that you can change. Maybe. Sure that remote start feature is nice, but sitting and idling burns fuel. And it doesn’t even warm your car up. Many small-displacement turbo engines can sit idling all day and barely make an impact on the temperature gauge. No, we don’t expect you to drive off with ice-covered glass – in fact, please don’t do that – but try and minimize idle time. That mass of snow and ice on your roof or in your truck bed isn’t just a hazard to the cars behind you, it can also cost you at the pumps. It’s heavier than you might think, and if it’s entrenched in your roof rack it’s not helping the finely-tuned aerodynamics one bit.
So what does it all mean? The EPA says that a gas vehicle can lose as much as 22 percent of its range at just -7°C. And it gets worse from there. Since hybrids, especially PHEV models, see the worst of both worlds, battery and engine cold effects, it can drop up to 34 percent. In a compact car that can mean moving from 5.9 L/100 km to 7.5. For an SUV, mid 12’s can turn into mid 14s. Electric cars can see similar impacts, with ranges cut by 30 percent, though that can be more impacted by how tolerant of the cold you are.
What can you do to increase your economy in the winter? Keep those tires properly inflated. Don’t idle your car more than necessary. Clear the windows properly, but don’t wait for the idling heater to do the work. If you have an EV, you get more options. For example, if the car is stored and charged in a warm garage, it can charge faster and take less time (and energy) to warm up the cabin.
We spoke with General Motors about keeping your EV warm and keeping up range. They suggested some tips that work on most EVs. Like preconditioning the car. The electric heaters work just as well when getting power from a plug. Preconditioning is setting the car to heat up before you get in. Then you have a full (and warm) battery and a warm cabin to come out to. Delayed Departure Charging is when you tell the car the night before when you’re planning to leave in the morning. It lets the car reach max charge just before you want to set off. That charging warms the cockles of the battery’s cold heart. Finally, once you’ve set off, the heated seats and steering wheel heat you more effectively than the cabin heater heats the air. So try and keep your backside warm instead of your nose.