How to save at the pump in spite of winter's effect on fuel economy

Temperature can have a profound impact on fuel economy.

(Thomas Trutsche / Getty Images)

As temperatures drop and gas prices rise, some bad driving habits could rapidly empty your tank.

Cold temperatures and winter weather can have a significant effect on fuel economy. With the national average for a gallon of gas up $1.31 from more than a year ago, any advice to help the wallet will go a long way.

According to AAA spokeswoman Ellen Edmonds, fuel line freeze-ups have all but disappeared due to modern gasoline. However, keeping your tank at least half full during winter in areas where temperatures regularly fall below freezing remains a good practice.

"It still reduces condensation in the fuel system, which is a good thing, and it also helps ensure that you will have an adequate reserve of fuel to run the engine for heat should your car become disabled in a remote location," Edmonds said.

The main problems people will have in bitterly cold temperatures are starting problems and coolant freezing up if antifreeze doesn't offer adequate protection, according to AAA.

Why is winter fuel economy lower?

Fuel economy tends to be less in colder weather for several reasons.

When the temperature drops, it increases the viscosity of engine oils, and other fluids increasing engine friction and requiring more time to reach normal operating temperatures. It also reduces battery performance, so the alternator must work harder to keep the battery charged.

"Cold air reduces tire pressures which in turn increases rolling resistance. Cold air is denser and increases aerodynamic drag which is especially important at highway speeds," said Stacy Davis, a researcher of transportation energy data at Oak Ridge National Laboratory who leads fueleconomy.gov.

Along with winter weather can come rougher driving surfaces due to snow, ice and gravel that reduce rolling efficiency. In many areas, the use of snow tires is recommended to improve traction, but they increase rolling resistance which lowers fuel economy, ORNL reports.

Also, winter gasoline blends may contain slightly less energy in a gallon of fuel than summer blends.

According to AAA, tire pressure is affected by cold air and can cause tires to become underinflated. In addition, the use of things like your defroster and heater requires extra energy, which equates to using more gas.

Cold air is also denser than warm air and creates more resistance for your vehicle to work against when driving.

Preparing your vehicle for freezing temperatures

• Check the level of antifreeze protection in your cooling system. If inadequate, it can cause coolant to freeze in the radiator during vehicle operation and lead to overheating. Coolant that freezes solid expands around 10% in volume and may cause cooling system or engine damage that can be costly to repair.
• If your battery is more than three years old, have it tested by a service professional to ensure it can provide adequate cranking power in cold weather.
• Make sure your engine is filled with the recommended motor oil. Most modern cars use multi-viscosity oils, and the first number in the rating is typically 0W, 5W, or 10W – which means the oil remains "thin" and flows more efficiently at lower temperatures.
• Check your tire pressures to avoid underinflation. Pressures typically decrease by one pound-per-square-inch for every 10-degree drop in outside temperature. Improperly inflated tires will impact fuel economy because it creates more resistance for the vehicle.
• If you drive a diesel vehicle, consider using a cold-weather fuel additive to prevent the formation of wax crystals that can plug the fuel system. The vehicle must be driven for a short time to circulate the additive throughout the fuel system before frigid weather sets in. The additive will not work if installed after the fact.

How to help your gas mileage in cold weather

• If possible, park in a garage – a heated garage is even better. This will help retain engine heat longer and protect the car from icy winds that accelerate heat loss.
• Preheat the cabin for hybrid or electric vehicles while plugged into the charger.
• Avoid excessive idling and warmup. A vehicle warms up more quickly when being driven but avoid hard accelerations until the engine is warmed up.
• Combine trips whenever possible. Short trips that require cold engine starts are the least efficient and, in the winter, it takes longer for the vehicle to warm up.
• For hybrid, plug-in hybrid and electric vehicles, it may be more efficient to use steering wheel and seat heaters than to heat the entire cabin. Read your owner’s manual for vehicle specific recommendations.
• Because of the increased aerodynamic drag in cold air, when it comes to carrying items on an exterior vehicle rack, roof-mounted racks decrease fuel economy much more than rear-mounted racks. When not in use, remove roof mounted ski racks and cargo carriers. This is also true for those who keep extra weight for winter traction. When not needed, remove all excess weight.