Ask a Technician: What Happens to My Fuel Efficiency During the Summertime?

May 20th, 2016 by


With the cost of fuel generally on the rise, savvy car drivers are always on the lookout for ways to improve gas mileage. There are many different factors that can influence your fuel efficiency. The car you drive certainly makes a big difference, but so does the way you drive, the road you drive on and even the weather conditions.

During the summer months, your car is likely to endure high temperatures and a lot of sunshine. So what impact will this type of weather have on your fuel efficiency?

As soon as the weather gets hot, most drivers are likely to reach for the air conditioning to cool them down. Many drivers believe that air conditioning may increase the fuel consumption, preferring instead to roll the windows down. By allowing fresh air to keep the car cool, you may believe that you are conserving energy. However, this idea may be untrue.

The Society of Automotive Engineers (SAE) conducted a study to see whether it was more fuel efficient to drive with the window down or to have the air conditioning on. What the study found was that when you drive at speeds of more than 55 miles per hour with the windows down, the fuel efficiency can decrease by more than 20 percent. Conversely, by having the air conditioner on and the windows closed, the fuel efficiency decreased by only 10 percent. By keeping the window or windows open, you will interfere with the car’s aerodynamics, causing more drag. This means that the engine has to work harder and consume more fuel to maintain the speed you want.

Therefore, when driving in summer at speeds above 55 miles per hour, it is better to have the windows closed and the air conditioner on. However, this may not be the case if you are simply cruising around town. At lower speeds, the study recommends that you switch the air conditioner off and open the windows. At these speeds, the engine is not producing enough energy to make the air conditioning efficient, so you will actually see better gas mileage if you roll the windows down. This may not be desirable in stationary traffic, but it is important to be aware that if the car is stationary, then fuel efficiency will suffer if you have the air conditioner on.

It is also worth remembering that driving a long distance in a convertible with the top down will drain the fuel faster than with the top up. The sunny weather and blue skies may make the convertible seem like a romantic option, but consider the significant increase that this will create in fuel consumption before you get too carried away. Keep reading our newsletter for more answers to your questions from the Mercedes-Benz of Princeton service department.

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