Measuring a Car’s Fuel Consumption
If you’ve bought a new car in Australia since 2009, you may have noticed a fuel consumption sticker in the window. This sticker shows the results of a factory fuel consumption test, giving details on the following:
- Urban: indicates city driving
- Extra Urban: indicates country driving
- Combined: indicates a combination of the two
Figures are shown in liters per 100km (L/100km) and, in theory, can be used to compare fuel consumption across different car makes and models. But how do they come up with that number, and is it accurate?
Official fuel consumption is traditionally calculated using a two-phase dynamometer test. The first phase lasts for 20 minutes and simulates driving in stop-start traffic. The second phase also lasts 10 minutes and simulates country driving, with an average speed of 63 km per hour and top speed of 120km per hour.
Of course, this testing system doesn’t account for real-world variables like weather and road conditions, which can also affect fuel consumption. So how can the average driver measure the fuel consumption of their car?
Measuring Fuel Consumption in the Real World
Measuring your car’s real-world fuel consumption is easy. Here’s how:
- When you fill up your fuel tank (until the pump clicks), zero out the trip meter on your odometer.
- Drive as normal until you next need to fill up – the tank does not need to be empty.
- Fill up, again until the pump clicks, and take note of how many litres you put in your car.
- Divide the distance you drove since you last fueled by the litres you just put in. This is your car’s fuel consumption in km per litre.
- To get L/100km divide 100 by the km/L figure.
Keep in mind that this figure may vary depending on the type of driving you’re doing, driving style, the condition of your car, and the weather. Measuring your consumption occasionally can give you a better sense of your car’s fuel economy.
Now that you know how to measure your fuel consumption, let’s take a closer look at the factors that can affect your car’s fuel efficiency.
- Service history: A car that is serviced regularly will likely have better fuel efficiency than one that has not been serviced.
- Weight: The heavier your car, the more fuel it uses. If you’ve made any modifications, such as added roof racks or a bull bar, it could affect your fuel consumption.
- Towing: Whether you’re towing a box trailer or a 17-foot caravan, it will cost you in fuel.
- Tyre pressure: If your tyre pressure is too low, your car may burn more fuel.
- Traffic: Frequent stopping and starting due to heavy traffic uses more fuel.
- Air conditioning: Love to crank up the air con on a hot day? Expect to see your fuel gauge drop more quickly.
- Driving style: Aggressive drivers who accelerate quickly and slam on the brakes will also use more fuel.
Decreasing Your Fuel Consumption
The less fuel you use, the more money you can save. While finding cheaper fuel prices is important, so are your driving and maintenance habits. Adopt good habits when it comes to your car and over time, you could drastically reduce the money you spend on fuel.
Choose your gear wisely
If you have a manual car, be sure that you drive in the correct gear. Staying in a low gear unnecessarily will use up excess fuel, as does pushing your car up a hill in high gear.
Driving an automatic? You can do your part by easing your foot off the accelerator as the car picks up speed, rather than pushing it into high revs. Also, practice improving your anticipation. Look ahead and be aware of cars braking or slowing down. Rather than waiting till the last minute to stop, take your foot off the accelerator early and ease into a smooth stop. When taking off again, slowly and smoothly speed up, rather than putting your foot down.
Stick to the speed limit
Got a need for speed? It’ll cost you in fuel consumption, especially if you drive at speeds above 90km/h. Use cruise control when driving on the highway to avoid fluctuating speeds.
Don’t be a drag
Aerodynamics aren’t just for aeroplanes. The more equipment you have on your car, the more drag it creates. Your car is forced to use more fuel to counteract these modifications, which can include open windows or sunroofs, surfboards on the roof, or awnings.
Fill up with fuel when your car is cool
You may have heard that it’s best to fuel up in the morning, when it’s cooler. It’s true that gas expands in the heat, though fuel tankers and storage tanks are insulated so fuel should remain cool at all times. However, when your car is hot, the fuel in the tank could create vapour, which could theoretically leave less room for the new fuel.
Inflate your tyres to the correct pressure
Check your car’s manual for information on the recommended tyre pressure. This helps maximise fuel efficiency and prevent wear on your tyres, so they’ll last longer.
Use the right type of fuel
With a range of different fuel types on the market, from E10 to diesel, how can you tell which one is best for your car? Refer to the manual or the inside of your fuel flap for advice on which type of fuel to use. If your manual suggests using premium unleaded, avoid putting E10 into the tank. It may save you money at the pump, but it can cost you over time. Some cars, such as those fitted with turbos, require different types of fuel to operate properly.
Go with the flow
Pumping the brakes and revving your accelerator are two practices that can use more fuel. Do your best to go with the flow of traffic and avoid putting yourself in a position where you’ll have to hit the brakes or pick up speed quickly.