We had a recent Raise a Hood customer interaction, concerned their fuel economy was dwindling as the temperatures drop.  No, the car is not broken, its behaving as expected. There are several reasons why virtually everyone sees lower MPG when visiting grandma over Christmas across the frozen northern climates, or simply headed to Flagstaff for some weekend skiing.  For a traditional gasoline engine that achieves 30 MPG in the summer, you can expect a 10-15% mpg loss, resulting in a winter efficiency of 25-27 MPG.  But why?  

Cold Effects on Engines (5-10% loss) 

There are two primary dynamics in play. First, cold starting engines take longer to reach operating temperature in winter and run less efficiently during this warmup period. Second, the engine fluids have higher viscosity when cold, this means engine oil, transmission fluid, and transfer case fluids are thicker and require more energy to rotate. Higher viscosity means increased internal friction and reducing efficiency.

Higher Rolling Resistance and Aerodynamics (2-5% loss)

Winter tires or snow-covered roads increase rolling resistance.  The tire temperature reduction alone will increase the rolling resistance 25-50% moving from an 80°F to 0°F.  The second reason is aerodynamic drag, we recently published an article of how the Ideal Gas Law impacts tire pressure during cold seasons, it is this exact same phenomenon that impacts winter driving.  Assuming the exact same atmospheric pressure, the air density increases as the temperature decreases.  Let your high school physics student run the calculations, and you will find that the air density increases roughly 8.5% over the same 80° temperature drop.  That also means it takes 8-10% more energy to move the car through the air than it does in summer. 

Accessories and Idling (1-5% loss) 

Accessories are in higher demand including seat heaters, electric defrosters, and less sunlight (higher use of lighting) all place an extra load on the engine.  Furthermore, we all know that in winter, idling your engine becomes a noble act of self-preservation - sacrificing fuel efficiency for the sake of staying warm and comfortable while patiently waiting on loved ones to, quite heroically, take forever.

Winter vs Summary Fuels (1-3% loss)

The difference between summer and winter blends is more than just chemistry—it’s a balancing act of performance and practicality. Winter fuel is formulated with more volatile components, specifically butane is increased from 2-4% to 10-15%. Butane is more volatile meaning it will be easier to start your engine on cold mornings. However, butane packs less energy per gallon than the heavier hydrocarbons used in summer blends. That means winter fuel inherently contains about 2-4% less energy, which is traditionally measured as the Lower Heating Value.  Before you start pointing fingers at the gas pump, modern engines do their best to compensate for the reduced energy density, adjusting air-fuel mixtures and ignition timing to keep you moving. As a result, the real-world impact on your fuel economy is closer to 1-3%.

Your Driving Habits (Impact varies) 

Snow, ice, or rain can force slower speeds and more frequent stops, which can either increase or decrease your fuel economy based on your specific conditions. Winter driving often involves shorter trips (who wants to ride their bike?) where the engine may never fully warm up, reducing efficiency further.

Everything above assumes a traditional gas engine, What’s the impact on other powertrains? 

Gasoline Vehicles: 10-15% MPG loss, for all the reasons outlined above. 

Diesel Vehicles: 5-10% MPG loss, diesel engines are more efficient in cold weather but still experience a drop due to similar factors.

EVs: 30-40% loss of range, EVs are heavily impacted by battery performance in cold weather and there is no residual engine heat to warm windshields and cabins; all heating drains the battery further.

To learn more about best practices for winter driving, check out our article on winter driving. 

Stay warm and drive safe this Holiday Season!