Do you ever have to do a double take when you pull into the gas station and see a low amount of miles on your trip display? If you think your trip display is playing games on you- you should know a few things about cold weather and your fuel economy.
I constantly hear complaints about fuel economy during the winter months- less miles per gallon or less miles per tank. Either way, its never fun looking down and realizing how lousy your fuel economy can sometimes get. I've had it too- last week I pulled into get gasoline and noticed "just" 285 miles on this tank of gasoline. That may be a lot for some folks, but I drive a four cylinder vehicle with a 13 gallon tank- pretty darn terrible fuel economy.
What gives? There are a few reasons that folks see lower fuel economy in the colder months. First, let's talk about where the engine comes in to play. Your car is designed to run at an high operating temperature. The colder it is outside, the longer it will take your car to be at its most efficient temperature, robbing your of mileage in the mean time. It's gotten quite cold here in the North Country lately, so this might be part of my (and your) problem.
Another significant factor is gasoline. Many times, states that see significantly colder temperatures in the winter have different gasoline throughout the different seasons. In the summer, the gasoline is a higher quality fuel that burns cleaner. In winter, the gasoline is more volatile and burns faster. This is also a reason why gasoline prices rise each Spring and fall each Autumn- the change to more expensive and cheaper fuel. Many times, this "Winter Blend" fuel contains more butane- an ingredient that burns quicker, resulting in slightly lower fuel economy. As temperatures warm, stations will be required to sell cleaner and slower burning gasoline, giving you back that better fuel economy.
Cold weather also results in a change in air density, which can lower the pressure in your tires, effectively increasing rolling resistance, and decreasing your fuel economy. If you're seeing a decrease in your MPG, I would advise you always to check your tire pressure and properly re-inflate tires if they are low.
Another note- markets in southern climates are slowly transitioning to the cleaner mentioned fuels. In many areas, only Summer gasoline is allowed to be pumped from terminals on May 1, and by June 1, it is the only gasoline allowed for sale at retailers. We'll see higher prices by then- if not because of the higher cost of the gasoline, then because of a combination of issues, including speculation.