Explained: E10 fuel

Ever since E10 fuel was introduced, there have been rumours about how it can be detrimental to a car’s engine.

The ‘E’ in E10 stands for ethanol (and the number that follows indicates the maximum percentage of ethanol). Ethanol is an octane booster, so E10 usually has a slightly higher octane rating than of 91 – nominally it’s 94 octane but it varies; in New South Wales, E10 is marketed as “Ethanol 94 (E10)”. The trade-off comes because ethanol produces about 30 per cent less energy than petrol, so chances are you will use slightly more of it for the same result. When ethanol is blended with petrol to 10 per cent, it will produce about 3 per cent less energy.

E10 is usually priced a few cents per litre below 91 octane fuel. Using the numbers above, you will only benefit financially using E10 if it is about 3 per cent cheaper.

In another article, we have discussed the need for a sufficiently high octane rating for your car’s engine. Octane is a measure of the fuel’s ability to resist burning too early inside your engine, an occurrence that will cause ‘pinking’ and damage at high revs or wide throttle openings. If your car is designed to run on 95 or 98 octane (check your owner’s manual or inside the fuel filler cap) it should not be run on E10. This is because of the sulphur content – premium 95 RON fuel has a maximum of 550ppm sulphur; 91 RON can have up to 150ppm sulphur). If the recommendation is 91 octane (or the recommendation doesn’t specify an octane rating but does state ‘unleaded fuel only’) you can use E10.

The vast majority of cars on Australian roads run on 91 octane.

Why do we need E10?
Most of the crude oil used to create petrol comes from overseas. Ethanol is locally produced, so diluting fuel with it makes good sense.

What about older cars?
Most of the concerns about using E10 are with older cars (broadly speaking, those built before 1986) – new cars can run on E10 because they have been designed to do so.

Generally speaking, it is not recommended to run any pre-1986 car on E10. Adding to the confusion, some post-1986 vehicles are also not suitable for ethanol-blended fuel.

Concerns about fuel with added ethanol come about because ethanol increases the ability of petrol to absorb water without separating. As a result, ethanol-blended fuel can contain more water and carry this through the fuel lines and engine. The greater the concentration of ethanol, the greater its propensity to hold water. And water, as we all know, causes corrosion.

The current thinking is that 10 per cent ethanol does not increase corrosion in everyday use.

In older cars, E10 has been known to loosen deposits in fuel tanks and fuel lines. This means the fuel filter may become clogged.

Ethanol blends have also been accused of causing deterioration of rubber components, gaskets, seals and hoses within an engine. Newer cars use compounds that resist this deterioration; older cars may not.

Some cars are listed as being E5 compatible. Using E10 in these may also result in material compatibility problems within the fuel system.

Why aren’t pre-1986 cars suitable for E10?
Prior to 1986, most cars used carburettors and steel fuel tanks. Ethanol-blended fuel’s greater propensity to absorb water increases the risk of corrosion in these components. The rust that results has the potential to block the fuel supply to the engine. Water in the fuel can also result in the engine running roughly and hesitantly.

Ethanol-blended fuel also has an effect on the air/fuel ratio because of the additional oxygen molecules in ethanol’s chemical structure.

Carburettor-equipped cars may experience hot fuel issues because the vapour pressure of ethanol-blended fuel will be greater (if the base fuel is not chemically adjusted) with an increased risk of vapour lock and hot starting problems.

Ethanol is a solvent that can attack unsuitable metal and rubber-based fuel lines and other fuel components.

Even cars using fuel injection are not immune. Ethanol-blended fuel has been known to result in premature deterioration of injector seals, delivery pipes and fuel pump and regulator.

What about emission levels with E10?
The more oxygenated ethanol-blended fuel may result in a leaner running engine and this, in turn, may have an impact on exhaust emissions.

Also of concern is that ethanol-blended fuel can increase permeation emissions from fuel system components. Components 20 years and older are at greatest risk. This leads to increased vapour pressure if the base fuel has not been chemically adjusted at the refining stage and increased evaporative emissions.

Is my car E10-compatible?
Modern cars will indicate in the owner’s manual or inside the fuel filler cap if they are E10 compatible. If you still aren’t sure, contact the manufacturer.

The FCAI has a listing on its website of the cars that are E5 suitable or E10 suitable. Check it out here

What happens if I put E10 into my non-compatible car?
It’s not particularly serious, but should you inadvertently fill a non-E10 compatible car with E10, there is no need to drain the tank. However, the best advice is to refuel with the correct fuel as soon as you have used one third or half of the tank.

The only possible problem you may notice is cold-weather start-up and driveability may be slightly affected.

What about E85?
Some vehicles (called flex fuel vehicles, or FFVs) have been designed to run on high ethanol blended fuel, E85. As the name indicates, this is 85 per cent ethanol and 15 per cent petrol (usually premium 98 RON).

Filling a non-E85 compatible car with this fuel can lead to serious engine problems, corrosion and increased exhaust emissions if the car is then driven.

In the unlikely event of filling up with E85, the vehicle should be towed to a service centre where the tank must be emptied and refuelled with the correct fuel. Some pundits suggest there won’t be a problem if you run it as usual and keep topping it up with regular petrol. It is probable that a ‘check engine’ warning will come on because the O2 sensors might detect fewer emissions and interpret it as the engine running lean. Running a normal engine on E85 is not something we’d recommend.

Originally published as Everything you need to know about E10 fuel on www.seniordriveraus.com. Republished with kind permission of the author.

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