What type of fuel should you fill your car with?

Cars need fuel to make them go, but knowing which fuel to use can be confusing. There are many different types of fuel available at the bowser, all at different prices and with some brands making bold claims about why you should use their fuel over others.

So which fuel should you use?

Your vehicle handbook or owner’s manual should tell you the manufacturer’s preferred choice of fuel for your car, but there may be other options available to you.

In this article we’ll explain:

What types of fuel are available?

LPG and diesel

If your car runs on liquefied petroleum gas (LPG) or diesel, those options are limited. There is premium diesel available from some service stations, but the RAC says this comes with no performance advantage, so it recommends sticking with regular diesel.

Petrol: regular and premium

When it comes to petrol engines, there are several options available.

They include petrol labelled at the bowser as 91, known as regular unleaded petrol (RULP), and 95 and 98, both known as premium unleaded petrol (PULP).

The NRMA said some premium fuels contain additives that may help clean your fuel system.

Leaded petrol is no longer sold in Australia, having been banned since 2002 due to its environmental and health risks.

What about ethanol?

Many service stations offer E10, which is a mixture of 90% unleaded petrol and 10% ethanol. The Queensland Government says the unleaded petrol component is normally RULP, but may be PULP in some cases. There is also E85, a blend of 85% ethanol, but as the NRMA says that’s reserved for very specialised cars and the Supercars racing vehicles.


What is the difference between 91, 95 and 98 petrol?

These numbers for regular and premium petrol refer to the Research Octane Number (RON) rating of a fuel.

Professor Shawn Kook, an expert in car engines at the University of New South Wales, told Canstar that RON is a standard measure of how well a fuel performs in an engine.

“Research Octane Number represents a fuel’s ability to avoid engine-damaging, abnormal combustion,” he said.

“This is called ‘knocking’.”

Knocking – also known as pinging or pinking – reflects the sound you may hear from your engine and could be a sign you are not using the correct fuel for your car.

“Higher RON fuels are designed to reduce the knocking and so higher RON fuel can help achieve higher engine efficiency and so lower fuel consumption,” said Prof Kook.

When it comes to which brand to choose, the RAC says it conducted a study of various retailers in Perth and found they all conformed to Australian standards and “no fuel brand was found to be consistently ‘better’ than others”.

When should you use premium fuel in your car?

Most new cars sold in Australia since 1986 were built to use 91, and recent petroleum statistics from the Australian government show it is by far the most popular fuel.

For example, Australian vehicles guzzled more than 9 billion litres of regular 91 fuel in the 2019-20 financial year. That compares to about 2 billion litres of 95, 2.9 billion litres of 98 and 2.2 billion litres of blended ethanol fuel.

But sales of premium fuels have been growing steadily over the years, as an increasing number of cars now require 95 premium fuel. Some high-performance models require 98.

Prof Kook said many high-end manufacturers design their cars to use only premium fuels.

“This means if those engines run on lower RON fuels, they will struggle with knocking, leading to potential engine damage,” he said.

Are there any benefits to using premium fuel?

You can use a higher-octane fuel than what is recommended for your car, but RACQ spokesperson Renee Smith said you may not see any benefit in performance.

The advice here is to do your own evaluation to see if using a higher RON-rated fuel than recommended gives you any improved fuel economy. Many modern cars allow you to track that economy by measuring the litres of fuel they use for every 100km travelled (L/100km).

This figure can vary, though, depending on the road conditions you travel in. For example, journeys on slow urban roads tend to be worse for fuel economy than faster motorways and highways. You might need to do several trips with the different fuels in the tank to see if you notice a difference.

You also need to take into account the increased costs of premium fuels.

“There could be small improvements in fuel economy,” Ms Smith said. “The higher cost of premium fuel needs to be considered, as this could cancel out any perceived or real benefits.”

The Australian Competition and Consumer Commission (ACCC) publishes quarterly reports on petrol sales and it has found the price difference between regular unleaded and premium fuels has been growing in recent times, as PULP has become more profitable for the industry.

In 2019-20, it said the annual average price differential between 91 and 95 petrol was 14.3 cents a litre, while the difference between 91 and 98 was 22.5 cents a litre.

The NRMA warned that fuelling an engine with 95 or 98 won’t necessarily improve performance or fuel economy unless the engine is specifically designed to run on those premium fuels.

The RACV has given similar advice and warns against paying extra for premium fuels if you see no benefit, unless a manufacturer specifies the need to use such fuels in your car.

There may be other benefits, though, from using premium fuels – they often contain more cleaning agents, which could help to keep your car’s fuel systems cleaner for longer.

Can you use E10 fuel in your car?

Ethanol is considered a renewable biofuel, typically made from grain, sugar cane or some other plant product. We’re encouraged to consider using E10 to help reduce potentially harmful exhaust emissions.

Most, but not all, modern cars can use E10, so it’s important you check first before filling up with E10 fuel.

The Federal Chamber of Automotive Industries says some E10 unleaded petrol blends are marketed as 94 RON. That means they do not meet the fuel standards for cars recommended to use 95 or 98 premium fuels.

Your car’s handbook should tell you if you can or can’t use E10. If the advice is still not clear, check with the manufacturer’s website or ask whoever services your car.

There are some checks online, such as the E10 compatibility check run by the New South Wales government.

Will E10 save you money?

E10 is generally slightly cheaper than regular 91 petrol but that price difference can change, and varies from state to state, and between regional and metropolitan areas.

The ACCC said the average price difference between E10 and 91 was just 0.2 cents a litre for the March quarter 2021, based on figures from across the five largest cities in Australia. Sometimes the average price of E10 is more expensive than 91.

The RACQ’s Renee Smith said E10 has a 3% lower energy content than 91, so you may find that you’ll use slightly more fuel to travel the same distance.

“To offset the increased consumption, you should look for E10 that is at least 3% cheaper than 91 petrol,” she said.

There are a number of websites and apps available that can help you check the price of different fuels types available near you. Examples include motormouth.com.au, petrolspy.com.au and petrolbuddy.net.au.

What if you fill up with the wrong fuel?

If you’ve accidentally put petrol in the tank instead of diesel, then don’t even start the car, the RACQ’s Renee Smith said.

“Doing so can increase repair costs by circulating the petrol through the fuel system,” she told Canstar.

If you’ve accidentally put diesel in the tank for a petrol engine, then the car probably won’t even start.

In both cases, the tanks need draining and refilling with the correct fuel. If you’re a member of a motoring organisation you can contact them for help, or contact your local garage or servicing centre.

Using a higher RON-rated petrol that is recommended is less of a worry. But if you’ve used a lower rated petrol than recommended for your car then you may experience ‘knocking’, or again you may need to get the tank drained and refilled with the correct fuel.

“Some vehicles specified for high-octane fuels will operate satisfactorily on regular unleaded but with reduced power and economy, while others risk extensive engine damage,” said Ms Smith.

“If the car is showing no signs of distress (no strange noises or poor running), it would be wise to drive gently (no hard acceleration, no towing etc.) while using up the wrong fuel and frequently topping up with the correct fuel until you have a tank full of the correct fuel.

“By using up the wrong fuel and continually topping up with the right fuel, you’ll eventually dilute what’s in there and get it back to what it should be.”


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