Why You Get Worse Gas Mileage in Winter: Unveiling the Truth

Why you get worse gas mileage in winter

As the temperature drops and winter sets in, many drivers notice their vehicles seem to be getting worse gas mileage than they did during the warmer months. This decrease in fuel efficiency can be puzzling, especially if your driving habits haven’t changed. However, it’s a common occurrence with a variety of contributing factors. In this article, we’ll explore why you get worse gas mileage in winter and what steps you can take to mitigate the impact.

The five main reasons you get worse gas mileage in winter

1) The cold engine metal robs heat from the combustion process, reducing combustion efficiency
2) Winter fuel contains less energy, so it takes more winter gas to achieve the same performance as summer gas, and
3) It takes more longer to bring the engine to full operating temperature, which uses more gas.
4) Cold engines create more friction
5) Generally, you use more electric power in winter to operate your window defogger, heater, and heated seats. You also run your headlights longer in winter due to the longer nights.

Cold Weather and Reduced Engine Efficiency

Engines operate most efficiently at around 200°F. So it takes more energy to heat a cold -10° engine up to 200°F than it does to heat a summer 90° engine to 200°. And, while a summer engine may cool to around 125° while you’re at work during the summer, that same engine will cool all the way down to -10° on a windy, blustery winter day.

So you’ll spend all that energy again after work to re-heat the engine back up to 200°. In other words,  every time you shut off the engine, whether at work or at the grocery store, you use more gas to bring the engine back up to operating temperature again.

Cold temperatures also thicken engine oil and other fluids, increasing friction and making the engine work harder. This additional effort requires more fuel, contributing to lower MPG.

Solution: To minimize this effect, avoid idling your car to warm it up for extended periods. Instead, start driving gently after a brief warm-up (30 seconds to one minute). Driving warms up your engine faster than idling. Also, ensure that your vehicle’s oil and fluids are appropriate for cold weather, as thinner oils can reduce friction and improve efficiency in low temperatures.

Winter Gasoline Blends And Reduced Energy Content

In many regions, fuel suppliers switch to a winter blend of gasoline as temperatures drop. Winter gasoline is formulated to be more volatile, meaning it evaporates more easily in cold temperatures. This ensures that the fuel can ignite properly in your engine, even when it’s extremely cold outside.

However, this increased volatility also means that winter gasoline contains slightly less energy per gallon compared to summer gasoline. On average, winter gas has 1.7% less energy than summer gas. As a result, your engine may burn more fuel to produce the same amount of power, leading to reduced fuel efficiency.

Solution: While you can’t control the type of gasoline available, knowing this factor can help you understand why you get worse gas mileage in winter. To counteract this, consider driving more efficiently—avoiding short trips that waste more gas and reduce idling time.

A cold engine reduces gasoline vaporization.

Engines don’t burn liquid gas. Instead, they burn gas vapor. In summer, the fuel injectors spray the liquid through small nozzles to form fine droplets. Then, the heat created during the compression stroke, along with the heat of the combustion chamber, causes the droplets to change state from a liquid to a gas.

On the other hand, a cold engine quickly dissipates the heat created during the compression stroke, robbing the droplets of the heat they need to change state.  To combat that problem, refiners convert to a “winter gas” in late Fall, and that winter formula includes more volatile components like butane and propane. Butane evaporates (changes state from liquid to gas) at just 33°F, and propane evaporates at -44°F, so it evaporates and ignites faster than summer gas.

A cold engine quenches the combustion process

Once your engine fires up, but before it reaches full operating temperature, the cold metal reduces combustion efficiency by quenching the burn before it’s complete. So, it takes more gas to keep your engine running, and that translates into lower gas mileage.

Oil thickens in cold weather, creating more friction

What more can I say? Cold oil creates a drag on the engine until it heats up to operating temperature. So it takes more energy to rotate your engine when the oil is cold, which is another reason why you get worse gas mileage in winter weather.

You have to generate more electrical power in winter, and that uses more gas

There’s no free lunch here. You run your heater, defogger, seat heaters, and headlights more often in winter than in summer. That means more electrical power, which means more gas.

What you can do to improve winter gas mileage

1) Don’t let your engine idle to warm up. It’s a waste of gas, and your engine will heat up much faster if you drive it than when you idle it.

2) Turn off electrical accessories sooner. I get it, you want your seat heaters on as soon as your buns hit the seat. But do you really them once the heater is blowing warm air?

3) Reduce the number of short trips in extremely cold weather. That reducdes the number of “re-heating” cycles on your engine and that saves gas.

©, 2020 Rick Muscoplat