Better Gas Mileage In Summer Than Winter

Hello Topspeed,
My car gets better gas mileage in summer than in winter. Any idea why?

Robin K. from Stamford, Connecticut

Hello Robin,

There are many factors that cause cars to achieve better gas mileage in warm weather. It is mostly due to the fact that cold weather, especially winter weather, negatively affects fuel economy in general. Some cars, such as hybrids and electrics, are affected more than others but this article will only address gasoline powered cars.

Here are nine reasons for why cars get better gas mileage in warm weather:

1. Oil Viscosity

Oil viscosity (thickness) is affected by temperature. Heat reduces oil viscosity (makes it thinner). This reduces drag on the engine and increases gas mileage. Cold increases oil viscosity (makes it thicker). This increases drag on the engine and reduces gas mileage. An engine operates more efficiently when the oil flows like water and not molasses. This concept also applies to all the other lubricants and fluids found in your vehicle.

2. Tire pressure and rolling resistance

In fall and winter, tires lose air pressure due to the colder weather. Under-inflated tires increase rolling resistance and decrease fuel economy. In spring and summer, tires gain air pressure due to the warmer weather. Rolling resistance decreases and fuel economy improves.

3. Engine warm up time

Modern vehicles achieve peak fuel efficiency only when they have reached their normal operating temperature. In colder weather, this process takes more time and results in decreased fuel economy. In warmer weather this is not the case. Your engine reaches normal operating temperature faster and fuel economy improves.

4. Air density

Hot air is not as dense as cold air and it presents less resistance to the forward movement of your vehicle. Consequently, your gas mileage will be better in warmer weather.

5. Ice and snow

Ice and snow, which commonly accompany cold weather, create slippery road conditions. This often causes wheel spin upon acceleration. A lot of wheel spinning also occurs when trying to get out of icy or snowy parking spots. All this going nowhere reduces your gas mileage. Furthermore, ice and snow force you to drive at less fuel efficient speeds.

6. Cold weather starting

It usually takes longer to start a vehicle in colder weather. In the middle of winter, poorly maintained vehicles can spend several minutes trying to start up. While the engine cranks, gas gets wasted and fuel economy decreases. Vehicles start faster in warmer weather which results in better gas mileage.

7. Winter grade gasoline

Here in America, many states require gas stations to sell oxygenated, reformulated, or blended gasoline during the colder months of the year. These types of gasoline often contain ethanol or butane, and this diluted gasoline will typically lower your fuel economy by one to three percent due to its lower energy content. Gasoline sold in warmer months has a higher energy content which results in better gas mileage.

8. Increased alternator and engine load

Drivers use more vehicle accessories in colder weather than they realize. The heater, the defroster, windshield wipers, electric seat warmers; all this puts an additional strain on the alternator. This demand on the alternator creates additional drag on the engine which reduces fuel economy.

9. Better vehicle maintenance

Many people are in the habit of tuning up their vehicles in preparation for travel during spring and summer. It is no secret that a well-maintained vehicle gets better gas mileage than one that is neglected.

Well, there you have it. Warmer weather equals better gas mileage. We can all move closer to the equator or we can wait until technology develops engines that are more fuel efficient in colder weather. Now wouldn't that be interesting?

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