Fuel myths & tips
The truth about octane numbers 91, 95, 96 and 98.
Fuel is rated according to its level of octane.
The octane number (or rating) is an indication of how much the fuel/air mixture can be compressed in the engine before it spontaneously ignites (i.e. the fuel ignites before it is lit by the spark plug). The higher the octane, the more resistant the fuel is to detonating early.
You need to use fuel with an octane rating that suits your car’s engine. If you use a fuel with an octane rating that is too low for your engine, you will get ‘knocking’ or ‘pinking’. In severe cases, this can lead to engine damage. Some high performance engines are very susceptible to knocking because they compress the fuel/air mixture more. These engines need higher octane petrol to prevent this.
The octane number is not a measure of the energy contained in the fuel. High octane fuels have the same energy per litre as fuels with lower octane numbers. If an engine is designed to run on low octane fuel, there is generally little or no benefit in switching to a higher octane fuel.
Fuel consumption rates on this website relate to the fuel specified by the manufacturer. Make sure you click on the fuel you use in your car to get the most accurate estimate of running costs.
Engine size is only a rough guide to fuel consumption...
...that’s why the figures on this website are a better guide to fuel consumption than engine size or weight. This chart compares the fuel consumption rates of different (European) engine sizes.
Generally, larger engines use more fuel than smaller engines, but within each engine size there is a wide range of fuel consumption rates. For example, you can see on this chart that the most efficient 3 litre engine uses fuel more economically than the least efficient 1.6 litre engine.
Tips – how you use your car does make a difference
- Slow down
As well as increasing accident risks, driving over the speed limit on the open road increases fuel costs by up to 10 percent. If you’re driving fast enough to be fined for speeding then the fuel cost will be significantly more. - Keep your load down
Carrying unnecessary weight in the vehicle increases fuel consumption, by around 2 percent for every 50 kg. So take those golf clubs out of the boot after the game, and remove the roof rack when you’re not using it. The same goes for the bike rack. - Think before you drive
Consider walking, cycling, or taking public transport before getting into your car. If you need to use the car, plan your journey. Picking up groceries and other items on the way home saves taking the car out later. - Avoid short trips
You use 20 percent more fuel driving when your engine is cold. - Drive smoothly
Make sure you accelerate smoothly. Change gear early (but don’t labour the engine). If you drive an automatic, choose ‘economy’ gear switching as this will keep the engine speed down. - Look ahead
Check what’s happening, maintain a safe following distance and you’ll keep at a more constant speed. This uses less fuel than accelerating and braking all the time. - Reduce idling time
If you’re going to be stationary for more than 30 seconds, switch your engine off. - Love your car
A little love goes a long way. Keeping your tyres at the right pressure saves fuel, as does checking your alignment, engine timing, air filter and spark plugs regularly. - Watch your air con
Only use air conditioning when absolutely necessary as it tends to eat fuel, up to 10 percent more in fact. Other features, such as the rear window demist, can also be a drain, so make sure you switch them off when they’ve done their job.
For more tips visit the www.energywise.org.nz website.