If you're into green driving and track your fuel economy closely, you probably know that cold weather can cause your car to require a little more gas. There are a lot of reasons for this. The biggest is that cold temperatures cause gasoline to thicken. That makes it difficult for the gas to combine with the intake air and provide the proper air-fuel mixture that an internal combustion engine needs. Not only is it harder to generate the correct mix, but it's also a little less powerful when the gas is cold. That means you end up using more gas to do less work.
The same factors are at play for hybrids and other fuel-efficient vehicles. While hybrids use their electric motors for slow-speed driving, their gasoline engines fire up when more power and speed are needed, and in cold weather, those engines are less efficient. What makes matters worse for hybrids is that because their engines aren't in constant use, in cold weather, it can take them longer warm up.
Think about it: Regardless of where you live, there's a good chance that you've gotten into a car on a cold morning. After a few miles of driving, even if those miles are driven slowly or in heavy traffic, the car gradually warms up. But in a hybrid, those few miles of driving may only use the gasoline engine part of the time, making it slower to warm up. That keeps the gasoline relatively cold and the engine running below maximum fuel efficiency.
But thickened gasoline and cold engines aren't the only effect cold weather has on eco-friendly driving. A lot of the time, cold weather means snow and ice -- and wet winter weather can have a negative impact on all cars' fuel economy, not just hybrids'. The negative effect comes from a couple of places. First, if an area gets a lot of snow, drivers are likely to use snow tires, which are heavier and have more rolling resistance than the typical low-rolling-resistance tires on a hybrid. That brings fuel economy down. Second, snow and snow-clearing chemicals can build up on the vehicle's exterior surfaces, blocking the grille and making it tougher for air to get to the engine. If the engine can't breathe well, fuel economy suffers. Lastly, if drivers don't clear all the snow and ice off their cars, it adds extra weight. Extra weight means fewer miles per gallon -- not to mention some pretty severe safety issues, too.