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Discussion Starter #1 (Edited)
Posted this elsewhere but thought you guys might be interested. 95 RON in the UK is equivalent to the US 91 Octane stuff I believe. We can't get any less than that at most forecourts.

Been tracking the fuel consumption on my Honda Insight ES (1.3 i-VTEC IMA) since buying it 5 months ago. I have the trip computer automatically reset each time the tank is filled. Generally been buying whatever is cheapest in the local area, or whichever garage I get to first after the fuel light comes on.

On supermarket (well - sainsburys, tesco and Morrisons) fuel the trip computer consistently reports 3-5 mpg higher mpg than calculated using the old brim to brim technique. Most of my fills have been at a supermarket with a few at the named brands.

For Shell and BP the computer consumption seems to be within 1-2 mpg of actual. It still over-reports the trip mpg but not by as much.

I'm going to try sticking to the branded fuels for a while to see if this holds true for a larger data set. I could potentially use Total, Esso or maybe Texaco too (though Texaco is unlikely as they're always about 4p more expensive than the others). Always been sticking to 95RON, as per the manufacturer's instructions.

I've seen people claim better mpg on branded fuels but always took it with a pinch of salt, as I figured the oil companies would be supplying the supermarkets anyway. Never seen anyone mention detecting a difference by calculated vs actual fuel consumption. Anyone else noticed similar.
 

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Discussion Starter #2
Update. My latest tankful from BP gave a 4mpg discrepancy between MID and calculated. That's roughly on par with the supermarket fuels so may just mean MID accuracy is a bit random.
 

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Ive noticed that for some time. I suspected it from my non hybrid vehicles, but I had no real proof. Now with the MID and scan guage I know for sure. It seems the cheaper places the gas is less efficient and gets less mpg, up to 5 in my experience. Then you got the content of ethanol. Some starts in the city have more, stations in the county and rural areas have less.

Of all, my car likes Shell best, then BP. My supercharged tacoma loved Shells V Power the best.

Sent from my Autoguide iPod touch app
 

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Ive noticed that for some time. I suspected it from my non hybrid vehicles, but I had no real proof. Now with the MID and scan guage I know for sure. It seems the cheaper places the gas is less efficient and gets less mpg, up to 5 in my experience. Then you got the content of ethanol. Some starts in the city have more, stations in the county and rural areas have less.

Of all, my car likes Shell best, then BP. My supercharged tacoma loved Shells V Power the best.

Sent from my Autoguide iPod touch app
yeh over the years i've came over to using shell 99% of the time.
 

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It is indeed true that the big oil companies supply petrol to the UK supermarkets. Petrol sold in the UK needs to meet British Standard 4040 (The Motor Fuel (Composition and Content) Regulations 1994) but the oil companies have more specific standards for their own-brand petrol.

For instance, Shell has one of the highest detergent fuels, which they claim keeps your fuel system and valve-gear cleaner, and indeed many motorists seem to agree.

'Off-specification' petrol that still meets BS4040 (or can be blended with other batches to make it comply) is sold on the oil spot-markets at a reduced price - and much of it is bought by the big supermarkets.

What all this means is that most oil company forecourts sell very predictable fuel that'll be the same every time, but supermarket fuel is less predictable: it could be just as good as the branded stuff, or it might have just scraped over the BS4040 spec.

Very unlikely that any of these fuels will damage your engine (because they all have to meet the minimum spec that was agreed with the motor manufacturers), but if you want consistent performance then Shell is probably one the best at the moment...
 

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I use Shell about 80% of the time. The other 20% is usually at a supermarket or RaceTrac (often the cheapest in the area).

And to Uriel's previous post, my last tank (from Shell) calculated tank average was also almost exactly -4MPG off compared to the MID.
 

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Discussion Starter #7
I've mainly been using BP and Esso recently (no Shell station without going out of my way). Up to 4mpg discrepancy between MID and calculated is seeming pretty usual.

To be honest I don't think there is a bigger discrepancy between branded and supermarket fuel when it comes to MID accuracy.
 

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I've noticed worse gas mileage with 89 octane vs the 87 I usually use. My buddy owns a gas station and he told me those numbers are the minimum it can be but usually test's higher when the state inspectors do their sampling. . He seen his 89 test 91 at times.
 

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Refinery blend components for higher octane gasolines tend to be less dense, there is actually slightly less energy per gallon as octane increases. This is one of the reasons that, if your engine does not knock, you should use regular gasoline and that higher octane gasolines waste money if not needed.
 
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