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To understand the different types of fuel, you’ll first need to know what an octane rating is. Octane measures how well a fuel can resist knocking, an uncontrolled explosion of fuel in the engine’s combustion chamber. If you’ve ever heard a knocking noise coming from the engine, that’s what we’re talking about.
The higher the octane number of a fuel, the more knock-resistant it is. Engines that require high-octane fuels are generally more powerful and fuel-efficient. Standard unleaded fuel in Australia has an octane rating of 91, while premium fuel is usually rated at 95 or 98.
Common Fuel Types
Unleaded petrol is the most common type of fuel for cars, followed by diesel and lesser-used fuel blends. ‘Unleaded’ simply means that the fuel does not contain lead, which can corrode a car’s engine.
Unleaded 91 is the most common grade of petrol for passenger vehicles in Australia, and tends to be among the least expensive. It is designed for use in cars, lawn mowers, motorcycles, chainsaws, and more. Most cars sold in Australia since 1986 can run off of Unleaded 91.
Unleaded 95 is considered a premium fuel, and costs more than Unleaded 91. It can lead to smoother engine running and better overall performance. All cars designed for unleaded petrol can take 95, though it may not make a noticeable difference in every vehicle. Unleaded 95 can be mixed with other grades of unleaded petrol.
Unleaded 98 is a high-performance premium fuel. Vehicles that require 98 will run more efficiently and have better fuel consumption when the correct fuel is used. It is particularly useful in vehicles equipped with knock sensors. Unleaded 98 can be mixed with lower grades of unleaded petrol.
Diesel is commonly used for light commercial vehicles and industrial transport in Australia. Diesel takes longer to burn and offers better fuel efficiency. Diesel engines have good pulling power (torque), which makes them ideal for towing. Diesel fuel should never be mixed with petrol as it can have detrimental effects on the engine.
You may occasionally see ‘high-flow’ diesel at the petrol station; although the fuel itself is the same, the pump and hose are larger, to allow for a faster flow. This is designed for use by large trucks with big fuel tanks.
Blends are now frequently seen in petrol stations, and can be a cheaper and more environmentally-friendly way to fuel your vehicle. The two main types of blends are diesel blends and petrol blends.
Unleaded petrol is sometimes blended with ethanol, a type of alcohol created by fermenting vegetable materials. Australia limits its petrol blends to a maximum of 10% ethanol (E10), though E85 fuel is an exception. Most petrol vehicles in Australia sold after 1986 can take E10, unless it requires 95 or higher.
E10 blends are cheaper, but the fuel economy is not as good. E10 blends use roughly 3% more fuel than regular unleaded fuel. As a result, E10 is typically 3% cheaper than unleaded.
E85 is an 85% ethanol and 15% petrol blend. It’s a less conventional fuel and would not apply to most vehicles. However, some drivers have their engines converted to run on E85. It is associated with reduced fuel economy but increased performance, and is commonly used in racing cars.
Biodiesel is a blend of regular diesel and alternative fuels made from materials such as vegetable oils or lard. Some vehicles can run entirely on biodiesel, though it is typically not recommended to use a blend higher than 20% biodiesel (B20). For the most part, vehicle manufacturers in Australia that do allow biodiesel do not recommend a blend of more than 5% (B5).
Biodiesel can be difficult to find and drivers should always check the manufacturer’s recommendations before using it.
How to Tell Which Fuel is Best for Your Car
How to Tell Which Fuel is Best for Your Car
When choosing a fuel type, the first port of call is the manufacturer’s guidelines for your car. Check the manual to see the minimum octane rating and fuel type for your car.
If the manufacturer recommends a specific type of fuel, that is likely the best type for your car. Although it’s not wise to use a lower grade of fuel than is recommended, it is generally acceptable to use a higher grade. Never mix unleaded petrol and diesel.
It can be hard to know what to do. Using a higher grade of fuel is more expensive at the pump, but does it translate to better fuel economy and engine performance? The answer is a little tricky, because it really depends on your car and your preference.
When weighing up your fuel, here are some things to keep in mind:
- Not all fuels are created equal. Although the octane rating may be the same, different fuel brands may use different additives or manufacturing processes. These can have an impact on fuel economy.
- Using a premium fuel may have a clear effect on some engines, while it may have no evident impact on others.
- Some cars require premium fuel, while others recommend it. Ultimately, you should follow the manufacturer’s instructions as putting in a lower grade of fuel could damage your engine.
- Cars that require premium fuel tend to be luxury or sport vehicles, such as:
- Certain types of Audis
- Volkswagen Passat V6 SEL Premium
- BMW 228i Coupe
- The older the vehicle, the less likely it is to respond noticeably to a high octane fuel. Older engines tend to be less sophisticated, and the benefits of premium fuels may not apply.