supermarket fuel

[John Rumm]

It also depends on the quantity of ethanol added - particularly on older engines.

[Chris J Dixon]

Back in the days of mechanical pumps there used to be a mechanical number display on the side, which was the actual total gallons dispensed, and a multiplication factor which was close (but not equal) to 1.

AIUI, because the pump accuracy was greater than the tolerance specified by Weights and Measures, it was possible to routinely dispense slightly less than was indicated. Not much, but enough to be worth doing.

Chris

[Chris J Dixon]

Back then, fuel prices seemed much less volatile, and it seemed much easier to predict whether it would be a cheap or expensive station by simply seeing the brand. Nowadays there really doesn't seem to be any predictability at all.

Chris

[Adrian]

You won't find any petrol that's less than 5% Ethanol, and - unless clearly labelled E10 - it cannot be more.

[Martin Brown]

There was also ICI petrol back then which for them was a refinery waste stream. Only problem with it was their petrol was much smellier than other brands but it was certainly cheaper!

I dunno about that - proximity to an airport, motorway services or on a dual carriageway pretty much guarantees spot price + 5p.

It is also a lot more expensive in the hills and dales where just getting the stuff delivered in bulk adds significant extra costs.

It used to be cheaper near major refineries too but I no longer live close enough to one to check this these days.

[Charles Hope]

Nearer 10p.

In the 1950 we holidayed a remote village in Scotland where the petrol arrived on the "steamer" in 50 gal drums. The deposit on the drums was less taht the cost of sending them back - so they ended up in the sea. The cost of the petrol had to allow for this. There was a road, but it was narrow and 3ply. The tanker drivers refused to use it, which is why petrol (and presumably TVO) had to come by sea.

[The Natural Philosopher]

Its not the technology, its how its actually implemented

the diagonal coupling between wheels made the austin 1100 handling 'interesting' to say the least.

But it was quite a smooth ride.

[The Natural Philosopher]

You still don't get it do you?

There is a world of difference between 'runs acceptably without damage' and 'best power output/smoothest running/best economy'

To take an extreme example. IF you add - say - nitromethane to your tank, you will without any retunes at all get a massive power increase.

Simply because its an oxidiser. it adds oxygen to the mix. So where a conventional engine might run out of breath the nitro engine will keep going to higher revs.

The shape of the bang - not just its timing - makes a real difference to power output and fuel economy.

All IC engines ignite before top dead centre, so a sharp bang then actually slows the piston down. You will optimise to get MOST of the ignition pressure after top dead centre where it does the most good, but automagically adjusting the ignition timing can only compensate so far.

A short sharp bang is not as efficacious as a longer slower one.

However the fuel mix and timing is only part of the story - the engine designer has compressions ratios, turbo boosting and combustion chamber shape to play with to affect the ignition explosion character.

And with direct injection these days, the injection can be more than once per combustion.

The final point being the engine is designed and mapped for one particular grade of fuel. And tested to ensure that others don't cause problems, but it is not optimised for them. All cars will run best on a particular grade and better or worse on others. And the RON number means nithg8ingm as any F1 aficionado will tell you. F1 fuel at one time was restricted to some RON number, but that didn't stop them putting in all manner of additives to constrict a highly toxic witches brew that gave a huge amount more power than 'pump fuel' of the same RON number would have dopne.

And that is why you get such widely varying reports as 'my car runs best on X' or 'my car ran worse on X' or 'my car runs the same on all grades'

Having a misspent youth tuning up small sports cars, I am particularly sensitive. One time I had a distinct vibration in my latest vehicle, a sort of engine thrumming at 70mph+. After refilling it at a different station, that disappeared.

Mind you the fuel pump was failing and did fail nearly completely some few hundred miles later, which may have been a contributory factor.

Basically if you actually care at all, try every single brand of fuel you can, and test them against YOUR car and YOUR driving style, and realise that its *more* likely that you will get a predictable fuel grade from a branded station than a supermarket.

Otherwise accept that if you fill up where its cheap, you *may* get reduced performance and shorter engine life on some or other components. Or you may not. It depends.

If you are driving a mass produced shopping trolley with 'tesco rash' dents everywhere that you will scrap at 100k miles anyway, well fine.

[The Natural Philosopher]

It still; is. Nearly all my refills exceed the 'total tank capacity' by quite a large margin.

In tease days of fuel filters I refill on a warning ligh + 40 miles.. :-)

[Huge]

Diesels don't pink and have no ignition timing. I also have severe doubts that premium diesel achieves anything whatsoever other than increasing the profits of the oil companies.

[Huge]

You and me both. And always have. Even in performance vehicles. There is an astonishing amount of c*ck spouted about this, especially given the subjectivity of people assessing their own fuel choices.

[The Natural Philosopher]

Wrong on both counts. Why am I not surprised?

Diesel 'clatter' IS pinking.. today's direct injection diesels vary the timing as part of the fuel mapping - when you inject is largely when it fires. And multiple injects per cycle can be done - that really helps with the low speed 'clatter'

That's as may be, but there are definite issues with using some grades of diesel in some diesel engines.

In particular biodiesel can lead to gumming of injectors and corrosion of seals and fuel pump and injector parts, and diesel that doesn't have additives may fail to absorb water and leave that at the bottom of the tank, or freeze up badly in winter.

'City Diesel' was designed for vehicles that do stop start type motoring and also IIRC features very low sulphur levels.

Marketing bollox is not all lies. Usually there is a grain of truth at the bottom.

[Huge]

Don't know about petrol, in this context, but I spent several years trying to ensure that there was as little overweight as possible in a number of snack products manufacturer by KP.

[The Natural Philosopher]

Petrol engines really don't like the *diesel* additive package.

I have no particular axe to grind, but even I find your total ignorance astounding. Fuel is not a single item. It is a blend of stuff including unwanted things like water, that has a definite and measurable impact on car engine performance.

All fuels are not created equal, that is established fact.

What is less definite is which fuels, if any, are reliably better, and in what way.

[Andy Burns]

There still are, you can gauge the relative volumes of unleaded, diesel, and "super" variations sold while you fill-up.

[Mike Tomlinson]

En el artículo , Huge escribió:

They claim it has increased lubricity and doesn't wax up as easily in very cold weather. No particular axe to grind, just saying that's how they justify the higher price.

Side note: diesel prices are on a par with petrol in the local filling stations, allegedly because of over-supply.

[Dave Plowman (News)]

The Allegro - in good condition - handled very well. Much better than many of the conventionally sprung cars of the day.

[Fredxxx]

Given that cracking a gallon of petrol takes a pint of oil, one can see why petrol should be more than diesel.

Shame the additional fuel usage for cracking isn't included on the CO2 per mile figures.

[Fredxxx]

I've heard others say the same about the Maestro.

[Adrian]

The Maestro was conventionally sprung.