Dear Drive… Is it okay to use 98-octane petrol in my car?

A reader asks:

With drivers looking for ways to improve fuel consumption and the overall efficiency of their cars, one question comes up all the time. Can you 'up' the octane in your petrol?

Many cars will print an advisory label on the inside of the fuel filler cap that notes the minimum fuel quality required by the engine, and while it's not recommended to go lower, is there any risk to going higher?

Bottom line, no. There is no risk when putting higher-octane fuel in your petrol car.

Drive spoke with Aleks Urosevic, an Expert Technologist at BP's Innovation and Engineering department, who noted that "Modern engines are more efficient [when using] higher-octane fuel and use less fuel [than an equivalent 91-octane rated engine]".

The octane rating of fuel is a reference to its resistance to premature detonation or knocking. The higher the rating, the less likely it is to combust under pressure, and thus the more suitable it is for high-compression and turbocharged engines.

"Engine manufacturers build into their engines a margin to allow for changes in the engine's octane requirement. Modern engines have knock sensors that can detect knock and adjust the engine operation to stop knock. Some have knock sensors that recognise higher-octane petrol and adapt to get the improved efficiency benefits," Urosevic said.

Most modern cars require a minimum of 95-octane fuel, especially if they are turbocharged. Stepping up to 98 in these instances will not cause your car any harm, and while the higher knock-resistance of the 98-octane fuel may lower any operating risks at higher rev usage unless your vehicle is tuned for a specific octane or is capable of recognising and adjusting to different octane fuels, the daily difference will be negligible.

This includes cars running on 91-octane fuel. The engines have been tuned to operate like this, and unless you are retuning your engine, there's no specific benefit to upping your octane.

Urosevic added, "It is therefore very important to use at least the minimum-octane fuel specified by the manufacturer for the engine, because modern vehicle computer systems are programmed to expect this.

"Using a higher-octane fuel provides additional protection if the engine is under load, and better fuel economy and power output if the engine has a knock sensor that can adapt to the higher octane."

Importantly, with or without a knock sensor, there's no risk to your engine.

That said, some high-octane fuels like BP Ultimate contain a higher concentration of cleaning agents in them. These are present in all fuels, and are designed to keep your fuel system clean of dirt and other particles that can form on critical engine components.

"BP Ultimate Unleaded (98RON) contains our best-ever engine cleaning technology," Urosevic said.

"The additive treatment in BP Ultimate cleans injectors and in addition inlet valves by removing harmful deposits. The BP Ultimate additive also contains additional components such as corrosion inhibitors to reduce corrosion of key fuel system components and so extend their life. Modern technology is using direct injection on gasoline engines (SIDI), and these can be prone to hard coke deposits not removed by conventional injector cleaners. BP Ultimate petrol can also keep these injectors clean."

Ongoing use of 98-octane fuel, with the increase in cleaning agents, will help to reduce carbon build-up on the engine's valves and injectors.

Don't suddenly expect your Corolla to perform like a Lamborghini, though. If the premium juice does end up cleaning your fuel system's internals, the car may start to operate more efficiently as it was always intended to.

Weigh all of this up with the added cost of premium petrol, and decide next time you are at the pump.

Just remember to keep to the golden rule of never using a lower octane than the car recommends and the higher octane will not cause any harm to your car.

Have a question about your next set of wheels or just need some car advice? No query is too big, small or obscure! Call in to the radio show (Trent on 2GB Sydney 1:30pm Monday and 9pm Wednesday, 5AA South Australia 1:30pm Tuesday, and James on 3AW Melbourne 9pm each Thursday), or contact us by email here: contactus@drive.com.au.