Can higher octane fuel boost your mpg?

[Fallguy]

Hi all,
Just wondering if anyone has tried higher octane (98 or 99 RON) fuel and compared the mpg with 95 RON unleaded? Apparently the Clio can use both so I am curious if spending a little more on fuel will actually save money in the long run?

[frv]

Chap I car share with swears by it - he has 2.0 Audi A3 and puts Tesco 99 RON in and says he gets another 5mpg and more power to boot. Costs 5p a litre more though so it's probably worth experimenting and if you don't notice much difference don't bother. The dealership actually told him the car runs better on higher octane fuel so it probably depends on the engine.

[Fallguy]

5mpg on a 2 litre Audi is quite impressive! I will give it a go next time I have to fill up.

[IanLorenc]

I was just looking at the maths on this.

Assuming the 5mpg increase is correct and 95r fuel is 99.9 and 98/99r fuels are 104.9 (I know they're not but it's just easier for calculations!).

10 litres of 95r would £9.99. If you then travelled 77 miles on that fuel, that would work out at 35mpg. You would travel 7.7 miles for each litre of fuel which means it would cost you 12.97p to travel one mile.

10 litres of 98/99r would cost £10.49. Assuming that - as per the claim - that fuel then boosted your economy to 40mpg, you would be able to travel 88 miles. That's 8.8 miles for each litre and a cost of 11.92p per mile.

That means that 400 miles of 95r fuelled driving would cost £51.88 but would only cost £47.68 using the 98/99. That's a saving of £4.20!
That's amazing!
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Sadly - whilst not wishing to call the integrity of your friend into question - I seriously doubt that switching to a higher octane fuel alone would really make that amount of difference...if any at all.

[Fallguy]

I have read elsewhere that higher octane fuel can get better
mpg, but by all accounts it only tends to be true for larger engine sizes. That would make sense with what your friend is seeing.

We'll see if I find any benefit - still a while before I need to fill up though!

[frv]

I thought he was exaggerating at 5mpg but he did seem to get more miles out of a tank and he boots it a bit! - definitely not a hypermiler, probably more like a hypermpg'er

[Fallguy]

If he has a heavy right foot, he probably gets better acceleration from the super unleaded, meaning he doesn't accelerate for as long to get up to speed and hence saves fuel.

Not sure what the term for a non-hypermiler is - hypermpger sounds very appropriate!

[Fallguy]

Nearly there - about a quarter of a tank left, so I
might put some super unleaded by the end of the week.

Hopefully this won't end in a smoking wreck of a car...

[Fallguy]

Right then, £20 of Tesco 99 RON in this morning, for a total of 17.41 litres. Given comparable mileage to unleaded that should take me to next Thursday ish.

A few thoughts on the 15 miles I have driven - the car seems a little bit more responsive and the engine is defintely running smoother and quieter. The only measurable difference thus far is the ability to shift into 5th at 28 mph rather than 30 without the engine straining.

[Karl]

I have only used high octane fuel (Shell Optimax) in my MR2 Turbo's. The MR2T was only available in Japan and therefore needed the "good Stuff" to match what the car is mapped for. Not using a higher octane fuel could cause issues with running lean.

As for use in UK cars - personally I think its poop. Its just another way of the fuel companies scamming even more out of the public for very little or no difference as they are not mapped for running richer fuel. Maybe its also psychological - it should be faster and therefore it feels it as you will put your foot down to test it.

I am very willing to be converted - esp if it will have me some monies!!