Maybe a daft petrol question

With that sort of difference because the forecourts tilted

to do a fair comparison you need to fill the tank completely, travel a couple of hundred repeatable miles (ie same load, same roads, same time of day) refill and check mileage, work out mpg. repeat for different petrol. You are very unlikely to get even a few percent difference between super and rubbish petrol.

my car can vary between 17 and over 40 mpg depending on the conditions it is used under, so the only way to determine true mpg for different fuels is to drive in a similar way on similar roads with the car in similar conditions. Sloshng in a tenners worth and driving till it's low won't give you accurate mpg.

mrcheerful

Obviously the higher the octane, the less of it you have to burn to get the same amount of power output. Hence, higher MPG.

But only if the engine can cope with the difference, and not all can.

You don't. Those are just comedy values that you've made up.

HTH

notice how i said Max, its only what i`ve notice on my computer over the passed 6 or 7 fill ups!

The difference is huge. It might not be impossible, but I would wager that there's a difference of driving involved here too. Or the vehicle is not designed to run on 95RON unleaded.

If you know better, just say so and explain why. Snooty posturing is a rather unnattractive trait.

Oh yes he will. It will invoke the conjunction of Mars and Jupiter and the well known magnetic properties of organic solvents. May even need a chicken sacrificed and it's entrails cast forth.

No amount of technical knowledge can compete with mumbo jumbo.

Actually there is a fiendishly cunning engine that uses a knock sensor to detect the grade of petrol and switch between hi and low octane fuel and ignition maps. Low octane goes rich to prevent detonation, closes the boost control bleed valve to reduce boost from 10psi to

6psi and won't open the "high load" butterfly plates in the shorter of the two ports on each cylinder to reduce the max power available. Has a distinct effect on fuel consumption. Didn't do that on UK ones just Japanese, seems like overkill until you know their low octane is 92 and hi 100 a somewhat bigger gap than the 95 to 98 we get here in the UK. Like going from 4 1/2 star down to 2 star in old star ratings.

-- Peter Hill Spamtrap reply domain as per NNTP-Posting-Host in header Can of worms - what every fisherman wants. Can of worms - what every PC owner gets!

Interesting.. though I can't say that I managed to digest that all!

As opposed to making an unequivocal assertion, and then dodging the request to back it up with some facts ? The URL provided by another poster covers just about everything.

Different driving for the first two, but on the last point I can't help but observe that I can get 44mph out of any fuel ;-)

Unlikely that the octane rating could account for the difference (unless your engine management is shot and is only giving the correct timing for

98RON fuel). The question of fuel quality has been rather done to death on this and other related newsgroups. It must all meet British Standards for octane rating and other things like sulphur content, but the chances of the calorific value varying so dramatically are small. (I will retract this if a refinery insider does turn whistleblower and admit they schedule production of decent petrol and "any old shit"...)

Forecourt tilt is another possibility. I had a rather uneconomic tankful myself recently, but when I checked my records discovered the previous one had apparently been uncommonly frugal. Underfilling by 3-4 litres would have explained the discrepancy. There are times when I can squeeze in that much extra after the first automatic cut-out, and times when it will hardly take another cupful. Observing the point at which the fuel gauge actually drops below full can reveal some significant variation.

Possibly to do with the locations of the petrol stations and the type of roads driven on to get home.

It's very unlikely that Asda and BP petrol are any different. Indeed they will all probably come from the same refinery.

Round our was all petrol comes from Fawley, regardless of whether it's BP, Asda or whatever.

The Ultimate stuff may burn slightly differently as they dilute it with various stuff before it goes on sale.

BTW, all these fuels with additives (Such as Ultimate) are a con. The petrol companies don't add the additives to make the fuel better, they add them to dilute the fuel. ie. they increase their profits.

sPoNiX

That won't make any difference to the fuel consumption. As worked out by the OBC, as the OP was asking. Only makes a difference to your wallet.

There will obviously be *some* tolerance allowed on the accuracy of a forecourt pump. But if a garage was found to have all of its pumps outside this tolerance, I'd expect them to be prosecuted.

Err, all petrol has 'additives'. If those additives 'diluted' the fuel, then Ultimate would give worse MPG than others, which is not the case. You'd also have to search far and wide to find an 'additive' that was cheaper than 'raw' petrol, and didn't cause problems...

consumption.

Dunno about dejectives, possessive or not, but using cheap petrol in my Volvo 740 2.0i automatic estate then using BP Ulticlimax showed no difference other than it seemed to run smoother/quieter. It still drank the same - like a fish, just did it quieter. Maybe a slight improvement in pick up, but along the lines of the difference between hot dry days and cold wet days when using the same fuel.

Stuart

I wonder if Peter can??????

Stuart.

Malt whisky comes to mind......... probably is cheaper these days lol.