What is ethanol?
Ethanol is an alcohol produced from plants such as sugar cane, corn and wheat; it is considered a renewable energy source. It is usually blended with unleaded petrol for use in cars.
There are national fuel quality standards for e85 and labelling requirements for ethanol blend fuel.
e10 is the most commonly available ethanol blend petrol, consisting of 10% ethanol and 90% regular unleaded petrol. The majority of petrol cars produced since 1986 are able to use e10 fuel. To see if your vehicle is compatible with e10 you should check your owner’s manual.
Ethanol has a lower energy content than petrol so you need more fuel to travel the same distance. RACV found that a vehicle running e10 would use around 3.4% more fuel.
Therefore, for e10 to be a cost-effective fuel it must be at least 3.4% cheaper than regular unleaded petrol. For example, if normal petrol were 150 cents per litre, e10 must be around 5 cents less to be considered cost effective.
e10 as a substitute for premium unleaded petrol
Some motorists use e10 as a substitute for premium unleaded petrol. e10 usually has a Research Octane Number (RON) of around 94, which is less than the minimum 95 RON for PULP.
Some vehicle manufacturers recommend that their vehicles are operated on 95 RON fuel as a minimum. Motorists should not substitute the premium petrol that their vehicle requires for e10 fuel, which may have a lower RON.
If you are considering using e10 instead of premium petrol, check with your vehicle manufacturer if e10 is a suitable for your vehicle.
In New South Wales, a certain percentage of all petrol sold must be ethanol. This mandate means that many service stations in NSW do not have regular unleaded petrol. Victorians travelling through NSW should be aware of this mandate and may have to use premium unleaded if their vehicle is not suitable for e10.
RACV does not support the introduction of an ethanol mandate in Victoria.
e85 is a blend of 85% ethanol and 15% petrol and is only suitable for "flex-fuel" cars which have the ability to sense how much ethanol is in the fuel.
Currently there are only a few flex-fuel vehicles on the Australian market that are able to operate on e85 fuel. These vehicles include some Saab, Dodge and Chrysler models, as well as some versions of the Holden Commodore and Captiva. Check whether your vehicle is e85 compatible with your vehicle manufacturer.
Some e85 blends are marketed differently and have varying amounts of ethanol from around 70% to 85%. The mixture ratio is varied throughout the year to ensure engines operating on e85 are able to cold start properly in the winter months.
Due to the reduced energy content of ethanol, a vehicle operating on e85 will use much more fuel than one using petrol.
Ethanol and water
When ethanol is blended with petrol there are no significant chemical reactions between the ethanol and the petrol and the ethanol simply mixes into the petrol. Over time the two fluids can separate and this separation is exaggerated when there is water present.
Ethanol absorbs water and when an ethanol blended fuel is put into a fuel tank, it will absorb any condensation or moisture in that container. This is not normally a problem if there isn’t much water or the fuel is used within a reasonable period of time, however if it is left to sit for a while the water and ethanol will settle to the bottom of the tank or container. This can lead to difficulty in starting an engine as the fuel in the tank is drawn from the bottom.
For this reason, ethanol blend fuels are not recommend for marine use and they shouldn’t be stored in containers for too long. Motorists should be wary of putting ethanol in an infrequently used car like a classic car.
Ethanol in classic cars
See RACV's fact sheet answering questions relating to the use of ethanol in classic cars.