Understanding Fuel Consumption

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With all of the changes in regulations regarding lower emissions and increased efficiency, it's becoming more important to fully understand exactly how fuel consumption works, so that it can be improved. To get a clearer picture, keep reading CARFAX's guide to understanding fuel consumption.

Measuring fuel consumption

Several things influence how much fuel a vehicle uses (and how quickly), including the engine parameters, weight, aerodynamic drag, and rolling resistance. Fuel consumption is measured around the world using a ratio of distance traveled per unit of fuel used. There are two general methods, using a fixed distance or a fixed fuel unit. The most common measurements are as follows:

  • Litres per 100 kilometres (L/100 km) — Used in: most of Europe, Canada, China, South Africa, Australia, and New Zealand
  • Kilometres per litre (km/L) — Used in: Some European countries, the Americas, Asia, Africa, and Oceania
  • Miles per gallon* (mpg) — Used in: the United States, the United Kingdom, and Canada (*U.S. gallon = 3.785 litres / Imperial gallon = 4.5 litres)

Gasoline vs. Diesel

The running costs of a gasoline vehicle versus a diesel can depend on the difference in price between the fuel types. Depending on where you live, one may be significantly more expensive than the other, or they may be almost the same.

Diesel engines have traditionally been known to be the most efficient for a few reasons. For starters, there is a higher energy density in diesel fuel. Thus, less is needed to achieve the same power-level as a gasoline engine. Other positive characteristics of diesel engines are their high torque (or pulling power) at low revs and that they can get into higher gears at lower speeds, which improves fuel consumption.

Gasoline engines are known to be quieter and are less expensive when buying the car. Although, both engine types are making advances in improving their weaknesses and the difference gap is slowly closing.

Technology which lowers fuel consumption

There are several other technologies, apart from the engines themselves, which can help improve fuel consumption. One must consider all of these factors when considering buying a car.

Hybrid drivetrains

The use of an electric motor in parallel to a conventional engine is quickly becoming more common among the vehicles in every automaker's lineup. Lauded for their excellent numbers when it comes to fuel consumption, hybrid vehicles really thrive in stop-and-go, as well as city, driving. Normally pressing the brake pedal is the enemy of fuel economy, but with a hybrid vehicle, the energy created through friction is harnessed for feeding the batteries. Thus it is recycled, rather than wasted, bettering fuel consumption.

Start-Stop systems

Many cars today also come with a start-stop option. The concept is simple: When the car is stopped (and in neutral) the engine turns off. When the driver presses the clutch, or moves into gear, the engine turns back on. Simple, yet very effective at improving fuel consumption.


Improved aerodynamics and low rolling resistance tires can be effectively used to lower fuel consumption. Many automakers are increasing focus on such measures, such as deflectors, underbody panels, and air-flow vents to help improve their vehicles' efficiency.

Fuel consumption and used cars

Often times, as a car ages, it loses efficiency. This can happen for a number of reasons, such as degradation of wires, belts, and plugs, carbon buildup, and problems with the exhaust. Additionally, vehicles which have been in accidents often have a drop in efficiency due to misalignment of the wheels and frame. When buying a used car, these elements become particularly important. Vehicles which have a clean accident record, and have undergone sustained and proper maintenance, usually stay close to their factory fuel consumption.

Check the CARFAX

For used vehicle shoppers who are focused on fuel consumption, checking the CARFAX Vehicle History Report can give you a detailed look at the vehicle's exact specifications, as well as its history, including service and maintenance records, accident history, structural damage, and much more. This information can help ensure you make the right choice when buying a used car.