WHAT should I put in my car E10 or unleaded?

It's a question asked often and to find out we've fed our Holden Captiva 7 test car five different kinds of petrol over the past weeks to see which is better.

The results might surprise you.

An attractively priced family wagon, the seven-seat Captiva was perfect for the job.

As well as E10 and standard unleaded, we expanded the test to include premium 95 and 98, along with the new E85 ethanol mix that some Saabs and Holdens can use.

There's nothing like being thorough.

The young feller at the counter of our local servo was a bit concerned when we told him that we'd just filled up with E85.

But we assured him it was okay, we knew what we were doing (some might disagree).

Seems some customers have mistakenly filled their cars with E85 with dire consequences if not designed to take the stuff.

Think rough idling and engine failure ultimately.

Holden has been making a big deal lately about its cars being E85 compatible, so our timing couldn't be better.

Mind you, try finding a servo that stocks E85 is not easy they're few and far between.

OUR TEST CAR

The Captiva 7 CX is a mainstream, seven-seat family SUV. Priced to sell from $38,490, it has a 3.0-litre V6 petrol engine, all wheel drive and a five-star safety rating.

The 3.0-litre V6, the smaller of the Commodore engines, produces 190kW of power and 288Nm of torque. It has a 65-litre tank and fuel consumption that is officially rated at 10.1 litres/100km giving it a theoretical range of 644km.

DID YOU KNOW?

Betcha didn't know the figures on fuel consumption stickers are based on premium unleaded 95.

If you're like me, you just go looking for the cheapest fuel you can find when it comes to fill up.

That's fine, but it means you're never going to see anything like the manufacturer's claim.

Sucks doesn't it?

The reason the test is based on premium 95 is that not all cars will take standard unleaded, especially European cars.

ETHANOL

Ethanol is a type of alcohol.

It is a renewable energy source and not as harmful to the environment as petroleum products.

The US Environmental Protection Agency says one litre of ethanol reduces net emissions of CO2 by over 90.9 per cent, so one litre of ethanol will save 2.11kg of CO2.

Most cars built after 1986 can safely use petrol with ethanol added.

In Australia, ethanol is made from sugar cane, red sorghum and the waste from starch production not from food sources.

In the past ethanol has been blamed for being corrosive.

But these days the ethanol sold in Australia must by law contain a corrosion inhibitor.

WHO'S RON?

Petrol carries a RON rating (Research Octane Number).

The higher the number, the more compression the fuel will tolerate before it detonates.

Generally fuels with a higher octane are used in high performance/high compression engines.

Most European cars are designed to run on Premium 95 RON unleaded because 95 is the standard over there.

If you run your car on petrol with an octane rating below that recommended you might notice a knocking, rattling or a pinging sound which means the fuel is detonating instead of burning smoothly. This can can damage your engine.

if you continue to use it.

URBAN MYTH

A trial undertaken in 1998 for the government showed that the use of E10 in vehicles designed for ULP increases fuel consumption by an average of 2.8 per cent but it varies from car to car.

The NRMA's technical expert Jack Haley said it was a widespread but misguided belief that if you used a high octane fuel your car's performance would increase. ``You won't achieve any improved performance from using higher octane fuels unless your vehicle's engine is designed for them," he said.

ULP

Standard unleaded has an octane rating of 91.

Locally produced vehicles, plus most Japanese cars, are designed to run on ULP and these don't generally benefit from premium or ultra premium petrol.

The NSW Government had planned to phase out ULP this year but bowed to pressure because motorists whose cars won't take E10 would have been forced to pay more.

Standard unleaded can however be hard to find and you might discover the unleaded that you're putting in your car already contains 10 per cent ethanol.

PULP

Premium unleaded petrol has an octane rating of 95.

Most European cars are designed to run on PULP because that is the standard grade of petrol overseas.

UPULP

Ultra Premium Unleaded Petrol has an octane rating of 98.

It's usually restricted to high performance sports cars.

Shell used to sell 100 RON petrol which contained 5 per cent ethanol but stopped in 2008.

E10

E 10 as its name suggests contains 10 per cent ethanol and has an octane rating of 94 or 95.

It is fast becoming the default as standard unleaded becomes harder to find.

In many cases it can be substituted for Premium in cars that require PULP.

E10 delivers a bit more zip than unleaded, but your car will consume E10 at a faster rate because it does not contain as much energy generally increases consumption by 1-3.5 per cent.

E85

E85 has an octane rating of 105.

It's the newest addition to our service stations but only a small number of cars can use it, including some Saabs and Holdens.

It is a cleaner-burning fuel that can enhance vehicle performance and reduce CO2 emissions by up to 40 per cent.

Although there is less energy in a litre of E85, which means less range than petrol, the ethanol component has a higher octane rating, so you may notice an increase in power and overall performance.

You might be surprised to learn that V8 Supercars have all run on E85 since 2009.

THE RESULTS

We clocked up more than 2600km over a four-week period, running the tank down to almost empty and refilling with a different fuel each time same car, same driver, same route. The prices quoted for fuel are all from the same outlet on the same day, which makes it a level playing field.

Apart from E85, there's not much between them in dollar terms.

We got the best range and best fuel consumption from premium 98 at 600km and 10.2 litres/100km.

But of course 98 costs a lot more.

The worst result came from E85 at 413km and 14.6 litres/100km.

So unless you're particularly committed to saving the environment, it's not the answer.

AND THE WINNER IS?

So, which is better E10 or standard unleaded? Ours was a real world test in real world driving conditions.

While the figures may vary between vehicles the relativities hold true.

As our test confirmed, expect better fuel consumption from ordinary unleaded at 11.1 versus 11.9 litres/100km.

Granted E10 is cheaper but the 2c a litre difference in price is simply not enough to warrant using E10 which costs $15.93 per 100km, compared to $15.08 for standard unleaded.

E10 would have to be $1.26 a litre or less to justify swapping 7c cheaper not 2c as it usually is.

E85 on the other hand would have to be $1.03 to make it worthwhile 15c less.

Based on our results you're better off sticking with standard unleaded, which will save you $170 over 20,000km or the course of a year.

But it's interesting to note that running the good stuff (98), jleven though it's more expensive, will set you back only 21c more per 100km or $41 over the course of a year.

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