Fuel Efficiency and How Your Car Works

Higher fuel efficiency is easy to understand and achieve if you know a little more about how your car works. If you want to save fuel, you should know the basics of energy conversion from the perspective of a car engine and drive train.

Frugal living doesn't require a lesson on physics, thermal dynamics or engine design, but knowing how your vehicle converts fuel into useful work will help you appreciate how to achieve greater fuel efficiency.



Let’s look at how the money you spend on gas is used in your vehicle. Used properly, it will save fuel. Used improperly, it wastes fuel.

• Your car performs energy conversion in several ways. It converts fuel (chemical energy) into other forms of energy that you can more readily use. If this is done efficiently, you save fuel.

• The basic forms of energy provided by your car are movement (mechanical energy); heat (thermal energy); and fans and lights (electrical and radiant energy). You pay for all of this when you buy a gallon of gas.

• Conversion from one energy form to another is always wasteful because energy conversion is never 100% efficient. For example, your radiator gets rid of engine heat that represents one of the fuel efficiency losses when you convert chemical energy (gas) to mechanical energy (movement). You are paying to heat the air with your radiator.

• Your engine has an optimal operating temperature at which it runs most efficiently. It takes many minutes and many miles to reach operating temperature, even in the warmth of summer.

• Sound, light, vibration and unburned fuel are also efficiency losses associated with energy conversion and operation of your car. You pay for these too.

• Friction (including wind resistance and braking) robs energy that would otherwise be used for work (movement).

• Your highest efficiency is gained by running your car in top gear. In top gear, the engine turns at a relatively slow rate (burns less fuel) while your car moves along at a relatively high speed (more work seen as movement). You save fuel by staying in top gear, known as over-drive for some vehicles.

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