CHOOSING the right fuel
Does the octane rating of the fuel you buy really matter?
We’re all starting to feel the squeeze at the pump from the recent hike in petrol prices.
With our regular 91 octane now exceeding the $3 dollar mark, it can be tempting for motorists to choose the cheaper option. However, it’s important to fill up your car with the octane type your owner’s manual recommends.
Using the wrong type of fuel in your car can be catastrophic for the engine. While most modern engines can adapt themselves to safely run on most octane levels, engines are optimised to use the fuel recommended by the manufacturer.
What can happen with the wrong fuel in the tank?
Inside an engine, a petrol/air mixture is compressed by a piston and ignited by a spark, with the resulting explosion pushing the piston down. If the petrol detonates too early, which can happen when using a lower octane fuel than the engine needs, it can try to force the piston down before it has reached the top of its stroke. This is noticeable as a rattling sound in your engine and can cause major damage if left unchecked.
Early detonation can cause
● Melted spark plug electrodes.
● Cracked piston rings.
● Melted or cracked pistons.
● Hammered rod bearings.
● Blown head gaskets.
Can you use any grade of petrol in a car?
The octane rating of petrol — 91, 95 or 98 in New Zealand — signifies its ability to resist detonation.
An engine is tuned to use petrol of a certain octane, and the higher the octane number, the more compression the fuel can withstand before detonating. Put simply, the fuel will burn at a different rate.
So, if your car requires 91 octane then that’s all you need, but you can use 95 or 98 octane petrol if you’re happy to pay more. If your car requires 95 octane you must use 95 or 98, but not 91. The bottom line is to use the recommended octane.
Are fuels sold by various brands different?
Vladimir Koutsaenko, senior adviser — fuel quality monitoring from Trading Standards (part of the Ministry of Business Innovation and Employment) says there’s not much difference. “The sampling and testing we undertake helps ensure that all fuels sold are in line with legal specifications. Some motorists are convinced that their car performs better on one brand of fuel than another. This is hard to prove or disprove. “Fuels sold in NZ are well suited for a variety of vehicles. Road and traffic conditions, along with other factors such as how a vehicle is being driven will have major effects on fuel consumption and performance. If fuels are advertised as having properties that make them superior, they must conform with the specifications when tested. If you are not sure if a fuel is suitable for your vehicle — such as ethanolblended petrol, which could be damaging to very old cars’ components — we recommend checking the owner’s manual or contacting the local agent.”
Why is fuel so expensive?
Automobile Association principal adviser Terry Collins says the Omicron outbreak, import costs
and supply problems are all contributing to higher prices. With European nations breaking ties with Russia, they will be forced to source their fuel from the same markets as NZ. This means prices will continue to increase. In an unprecedented move, the Government announced that from
11.59 pm Monday 14 March 2022 there would be a temporary reduction in the fuel excise tax by
25c per litre for three months. The
25c cut is on the fuel excise duty, not on the GST. It’s expected the tax cuts will save Kiwi motorists between $11 and $17 for a full tank. The temporary reduction has been introduced as part of a cost-ofliving package — aimed at giving NZ families immediate relief through the current global energy crisis triggered by the war in Ukraine.
Is NZ’s fuel quality better or worse than in other countries?
Our fuel quality specifications are in line with those in similar economies like Australia, the US, and the UK. Koutsaenko says: “There is a Worldwide Fuel Charter that sets out car manufacturer expectations and requirements for fuels, to help ensure compatibility with the vehicles produced. Fuel specifications are periodically updated, reflecting developments with vehicle technology in response to environmental and health requirements.”