Which petrol should I use?
The numbers are what matters. Standard unleaded petrol is 91. Premium unleaded is both 95 and 98. The ethanol-blended E10 (a mixture of up to 10 per cent ethanol in petrol) is a substitute for 91 in most cars 2005ish or newer. However, it pays to check your user manual.
Those numbers – 91, 95 and 98 – are the so-called ‘octane rating’ of the fuel. They’re all about the same in terms of the energy in the fuel. What octane really is, is an index of a fuel’s resistance to burning too early inside your engine – if that happens, it causes ‘pinking’ or ‘pinging’ (same thing), which is mechanically destructive at high revs and large throttle openings.
Carmakers design engines for a minimum octane rating. If you open the fuel flap of your car and it says ‘unleaded petrol only’ it means 91 octane fuel is OK. If the fuel flap says ‘premium unleaded only’ it means you need to use at least 95. If the fuel flap tells you to use 98, that’s what you need to do.
It can’t hurt your engine if you use a higher octane fuel. So, for example, if you use 95 or 98 in an engine designed for 91, that’s OK. However, it’s not acceptable to put in a lower octane fuel than the minimum recommended by the manufacturer. Using 91 in an engine designed for 95 or 98 is potentially destructive.
If you run them on a higher octane fuel than the minimum recommended, you will get either better economy or more performance (depending on how you drive). But in practice, the improvement is tiny, and the price premium of the higher octane fuel often eclipses the economy benefit from running it – in other words, it’s not an economically rational choice to run 98 in an engine designed for 91, even though it might run slightly better. However, you might have to do your own maths on this one:
- If you find you get 10% fuel economy, say, from 98 and the price difference at the bowser is less than 10%, then you might find it better to fill up with 98 as it probably delivers savings in the long run
However, 98 is often a fair bit more expensive than 91, nullifying the benefits. Many modern cars don’t even need to run on 91 anymore, and can instead rely on E10.
What is E10 petrol?
E10 fuel is a blend of up to 10% ethanol with 90% unleaded petrol. Ethanol is an alcohol, and is ‘drinking alcohol’, so it’s the alcohol found in your favourite drink. E10 petrol is actually a slighter higher octane (94) than regular 91 in a lot of cases, and that can mean your engine performs better. However, ethanol lowers the energy level of the blend by 30%, which means you may experience a slight loss in fuel economy.
The slight loss in fuel economy could be offset by the cheaper price of E10 compared to 91. In addition, you may also be helping to prop up the Australian sugarcane industry, instead of sending your money to Middle Eastern oil barons. Ethanol is made from sugarcane – and corn, among other crops – and boosting demand for such a resource may help out sugarcane farmers in Queensland. So you can possibly get a performance boost, potentially spend less at the bowser, and help out Aussie farmers – what’s not to love? Keep in mind, though, that your car will have to be compatible with E10:
- The Queensland Government has released its ‘E10 OK’ campaign, where you can type in your registration and find out if your car is compatible. Note that only cars made post-2000 are in the database.
- With this tool you can also find out what stations stock E10 near you.
E10 is just the first of what’s to come with ethanol-blended fuels. E85 may be the next step in the ethanol fuel evolution.
What is E85 petrol?
E85 petrol goes further than E10 and features a blend of anywhere between 50 to 85 per cent ethanol. Nicknamed ‘flex fuel’, E85 once again boosts octane levels – this time to 100 octane. It is for this reason it is commonly seen as a racing fuel, and the Supercars’ V8 Holdens and Fords also use E85. This is for its performance characteristics, but like E10, the energy density is lower than regular unleaded, and fuel economy is potentially hampered by up to 30%. E85 is favoured by revheads, performance car owners and track enthusiasts alike. However, finding E85 fuel is currently a bit of a hard task.
Where can I find E85?
The most common fuel station in Australia to have it is United Petroleum. United says the ethanol component is produced by itself at the Dalby Refinery in Queensland, and is sourced from Sorghum Grain. E85 is commonly cheaper than regular 91, but once again, you’ll have to have a compatible ‘flex fuel’ vehicle. Newer, performance-oriented vehicles may be compatible.
What if I use a lower octane fuel?
Fuel retailers love to talk up the purported benefits of their premium fuels. They don’t lie on this, but they do overstate the benefits. Most modern engines have the ability to adapt either down or up depending on what fuel you use. That means if you use a lower octane rating than recommend, it might not kill your engine, but you might experience the following:
- Loss of power or acceleration
- Loss of fuel economy
- Pinging or knocking in some scenarios
Modern engines generally have the ability to ‘detune’ based on what fuel it detects is being used. This is likely to result in the two former points. However, if you have a high-performance car that needs 98, chances are putting in 91 or E10 could cause knocking or pinging. Inside your fuel flap, or in the user manual is where you’ll likely find what type of fuel you need to use.
What should I do if fuel causes my engine to knock or ping?
Using the correct fuel causes proper timing and ignition in the combustion cycle; using a lower octane fuel than recommended can throw this off and create knocking, or pinging. There are some things you can do to save your car from knocking:
- Use an octane booster: These are usually available in 500mL bottles or so from auto stores, and cost around $20.
- Use a fuel flusher: Again, these are available from about the $20 mark, and help to clean injectors, combustion chambers, inlet valves and manifolds.
If your car has no signs of pinging or knocking, your engine could be adapting to the new fuel, but be aware your car may not see as good a fuel economy or acceleration as normal. In this instance drive until the tank is empty and then fill up with your recommended fuel.
What octane petrol does my car need?
Below is a list of the top ten selling cars on Australian roads at the time of writing, with a guide of what type of fuel to use. Note that the fuel recommended is a minimum standard, and many performance versions of particular models probably require higher octane fuel. The advent of small, economical turbocharged vehicles has also seen the rise of premium fuel use.
It’s interesting to note that the top ten selling cars generally take only 91, instead of demanding the more premium drops of fuel. Many of the ‘work-oriented’ vehicles also seem to demand 91, instead of E10. However, you should be aware there are many different specifications within a model range, so your particular car may require a different kind of petrol. Also be wary that many of these models also come in diesel, so fill up with the right fuel! If in doubt, check your car’s user manual.
Petrol Octane: The Last Drop
No matter which petrol your car needs, it’s important to choose the right one. Many modern vehicles can run or E10 or 91 with no serious ill effect. A full list of cars can be found here. However, if you’re doing it to save a buck or two, you may be misguided. Often putting in a lower-quality fuel can hamper acceleration and fuel economy, so you may pay for your choice in other ways.
Manufacturers don’t recommend a minimum fuel quality for no reason – often the engines demand it to run in tip-top condition. This is especially true for performance-oriented cars. No matter if you’re dropping the kids off to school, or taking your car to the track, it’s important to use the right fuel – check your user manual if unsure. Even though today’s engines can take on a lower quality fuel, you may find the cost benefit in the long run not worth it.