Brad Panovich: Why cold weather gives you lower gas mileage

<b>Brad Panovich: </b>Why cold weather gives you lower gas mileage

Billy Graham Parkway


by Brad Panovich / First Warn Chief Meteorologist

Bio | Email | Follow: @wxbrad

Posted on February 21, 2013 at 12:34 PM

Updated Friday, Feb 22 at 6:21 PM

CHARLOTTE, N.C. -- With gas prices soaring, you really need to watch every gallon of gas you use. I know I am kind of OCD about my miles per gallon in my car. I used to keep track of it on my iPhone and track it over time since last year when I got a new car, which now keeps track of it for me right in the on-board computer.

So, like many people, you probably notice you get worse gas mileage in the winter than in the summer. The biggest reason for this is the cold air. The ideal operating outside air temperature for your best MPG’s will be from 75°-85°. Once you start dropping below about 68° the mileage decreases pretty rapidly. In fact depending on your make and model your mileage could drop by as much as 22 percent from summer warmth to winter cold.

So why such a big difference? Here are some of the main reasons why.

#1 More Idling:

Idling burns gas with no MPG’s so it’s the worst thing for mileage. In the winter many people warm their cars up, which just wastes gas. Most cars only need about 30 seconds of idling before they are ready to go. Cars also will idle at higher RPM’s to warm the engine up faster in cold temperatures versus warm, which also uses more gas. People leave cars running more to keep warm, thus burning more gas as well.

#2 Lower Tire Pressure:

For every 10° drop in air temperature outside your tires will lose 1 percent in PSI or inflation. For every one PSI that your tires drop in pressure, you will lose about 0.4 percent in fuel economy. So if your tires are under inflated by three PSI your car would go from getting 22 mpg to 21.7 mpg.

#3 Lower Engine Temperatures:

Your ideal engine temperature is around 150°-195° depending on your make and model. Most modern cars with computerized management systems for the engine will order up more gas in the combustion camber to compensate. More fuel is added to the air/fuel mixture when the engine is cold. Parking in a garage or combing trips when the engine is warm which will help reduce this.

#4 Higher Oil & Lubricate Viscosity:

When your oil and oil pan are cold your oil becomes sticky and takes more energy to pump through the engine. Transmission and differential fluids do the same thing. Using synthetic fluids can help reduce this problem, along with the garage or combining trips.

#5 Higher Electrical Usage:

In colder temperatures:

-  You use your lights more because it’s darker earlier.
-  You use window defrosters more, seats heaters and mirror heaters.

#6 Weaker Gasoline Blends:

Gas doesn’t like to vaporize at colder temperatures so oil companies change the gasoline blend  differently for cold weather markets. These changes make gas work better in the winter and at colder temperatures but it also decrease MPG’s.

#7 More Aerodynamic Drag:

When it’s cold you have more drag on the car as the air passes over it. Cold air is just denser than warm air. A vehicle’s aerodynamic drag is proportional to air density, and the density increases as temperature drops. For every 10°  drop in temperature, aerodynamic drag increases by 2 percent.

#8 Icy or Snowy Roads:

Cars that have slippage on their tires burn more gas. Now we don’t always have to worry about this but it is a small factor. Plus if you have automatic AWD/4x4 and it kicks in while on slick roads you are using more gas.