Your burning questions about fuel, answered

Q. Is it better for my car to use premium petrol even if it’s not recommended for it?

A. If you’re pumping petrol into your car that is a higher octane than the one recommended by the manufacturer, say 98RON into a 91RON car, you’re just burning extra money that you could spend elsewhere. Higher octane petrol can provide some slight performance and fuel economy improvements in vehicles that can adjust for it, but any slight savings in fuel will be chewed up by the significantly higher price you’ll pay per litre. It’s best to just use the fuel type recommended by the car’s manufacturer. So, if yours uses 95RON, stick with that.

Q. Is fuel from some fuel brands better for my car than others?

A. Results from fuel testing by RAC at different fuel retailers in the Perth metropolitan area showed all fuels were within legally required specifications. While there was some very slight variation within required boundaries between brands and sites, no fuel brand was found to be consistently ‘better’ than others in its basic form. Australia also has national fuel standards which cover fuel sold at all service stations in WA. When it comes to fuel contamination, such as fuel being mixed with water or other fuel, instances of this are very low.

Q. Is it ok to use a lower octane petrol than the one recommended for my car?

A. No. Using petrol that is a lower octane number than the one recommended for your car can cause engine damage and void your car’s warranty. The RON, which stands for Research Octane Number, indicates the fuel’s anti-knock threshold. When you use 91RON fuel in a 98RON car, you may hear a ‘knocking’ or pinging sound. This is the petrol detonating uncontrollably rather than burning at the right time in the right way. Choosing a lower octane than you need may save you some money in the short term, but it’ll cost you much more down the road.

Q. Some fuel companies claim their fuels clean engines – is this true?

A. We’ve seen no independent research to verify the claims by these companies about the engine-cleaning capabilities of these fuels.

Q. Why are fuel prices higher in the country than in the city?

A. There are a number of reasons why fuel prices may be higher in regional areas compared with Perth. The cost of transporting fuel over greater distances into regional areas is one reason. Reduced competition outside the Perth metropolitan area also has an impact. Without other fuel retailers nearby to compete against, there is less incentive to keep prices down. Regional fuel retailers generally sell lower volumes of fuel than their metropolitan counterparts. Also, because there is no weekly petrol price cycle in regional areas as there is in Perth, prices don’t tend to fluctuate as much, meaning less opportunity to save on cheaper fuel days.

RELATED: How WA's fuel prices are determined »

Q. What happens if I accidentally put the wrong fuel in my car?

A. It depends on the fuel and the car. Putting 95RON or 98RON petrol into a car that only needs 91RON will cause no damage other than to your hip-pocket. But using fuel with a lower octane than the one specified by the car’s manufacturer will damage the engine over time. Worse still, pumping petrol into the tank of a diesel vehicle and then driving it can cause catastrophic damage to the engine. If you do pump petrol into your diesel car, don’t drive it. Call RAC Roadside Assistance to organise to have it towed to a workshop where it can be drained. RAC Auto Service Centres have specialised pumps that can drain the tank. With seven different types of fuel sold in WA and not all retailers using the same labelling and colour coding, it’s important to pay attention at the pump.

Q. Is premium diesel better than standard diesel and should I buy it for my car?

A. We have not seen any independent, scientifically derived evidence that some premium fuels clean engines as is sometimes claimed. Premium diesel fuels have the same cetane number as regular diesel, so there would be no performance advantage in using this fuel over regular diesel. For this reason, we would recommend saving your money and just using regular diesel.

Q. Does fuel have a ‘best before’ date?

A. According to one fuel company, the useful life of petrol can be as little as one month. Using a vehicle containing old fuel can reduce performance and cause rough running. So, if you’re going away for longer than a few weeks, leave your vehicle’s tank around one third full then top it up with fresh fuel when you return. Diesel fuel can last for up to one year, but aging diesel fuel can suffer from the formation of gums and sediments and the growth of fungus. This can be treated with a diesel fuel conditioner.

Q. Whatever happened to LPG?

A. LPG was once a viable fuel when LPG was cheap, when there was no excise on it and when State and Federal subsidies for LPG vehicle purchases and conversions were available. LPG was also more viable when petrol and diesel vehicles were less efficient and before hybrids became more affordable and widespread. As no dedicated LPG vehicles are now sold in Australia, and the number of LPG retailers is continuing to decline due to low sales volumes and ongoing infrastructure maintenance costs, the number of LPG retailers is also declining. Although LPG still has good environmental credentials, it is less economically attractive for the above reasons, a factor magnified further by the higher litres/km consumption rates LPG vehicles often achieve.

Q. Can I really save money by monitoring fuel prices in Perth?

A. Perth has a petrol price cycle which sees prices rise and fall across a specified period of time. Previously this cycle was weekly but it is now fortnightly. In 2018, Perth motorists who filled up at the lowest-priced fuel retailers throughout the year could have saved an average of $211 across the year, according to a report from the ACCC. To find the cheapest fuel in your area, visit fuelwatch.wa.gov.au. You can also sign up to receive email notifications from FuelWatch showing the cheapest locations in your nominated areas. The ACCC report also found that independent fuel retail chains offered lower petrol prices than the major petrol retailers.

Last updated: October 2021