Supermarket diesel

ubersonic said:
Its complicated but basically when you buy normal/super from BP its 95/97 octane, when you buy it from somewhere like sainsburys its something like 93/95 octane mixed with an octane booster called ethanol to raise it to 95/97. Its cheaper than petrol of X grade but as ethanol has a lower calorific value than petrol (there's less energy in it) your car will not go as far on say Tesco unleaded as it would on BP unleaded. Tescos 99 sounds great but its 10% ethanol (the maximum allowed under EU law) so unless you really need 99 octane you would be better on BP/Esso super.
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The calorific value of ethanol is irrelevant in the point you are making, especially on standard unleaded across the suppliers...
As they almost ALL use ethanol in their standard unleaded.

What BP DONT do, is have ethanol in its super unleaded petrol.

Ethanol is primarily used as a bio fuel additive, not as an octane booster.

The octane rating of fuel doesnt correspond to the amount of power it produces, merely to its resistence to detonation.
If you use a higher octane fuel than a car requires, you will in theory, use more fuel.
 
atpbx said:
The calorific value of ethanol is irrelevant in the point you are making, especially on standard unleaded across the suppliers...
As they almost ALL use ethanol in their standard unleaded.
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As my point was that fuel with ethanol will give a lower mpg than fuel without due to the lower calorific value of ethanol, and this ethanol fuel is cheaper because its lower quality (and can damage classic cars as a result) I think its pretty relevant >.>


atpbx said:
The octane rating of fuel doesnt correspond to the amount of power it produces, merely to its resistence to detonation.
If you use a higher octane fuel than a car requires, you will in theory, use more fuel.
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Yes, that's what I said.
 
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The basic petrol/diesel, pre-additive, is the same whether it's Shell, BP, Tesco etc as there are only so many refineries in the UK and the specs are pretty tight. Often one refinery will supply most filling stations in a particular area.

What does vary are the additives the various companies put in their fuels. However, as they tend not disclose exactly what additivies they use it's difficult to tell which fuels are better/worse with any certainty.
 
ubersonic said:
As my point was that fuel with ethanol will give a lower mpg than fuel without due to the lower calorific value of ethanol, and this ethanol fuel is cheaper because its lower quality (and can damage classic cars as a result) I think its pretty relevant >.>




Yes, that's what I said.
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No you didnt.

You say you will go less miles on Tesco unleaded than you will on BP unleaded because Tesco unleaded contains ethanol.

BP standard unleaded contains Ethanol.

Its also not used because its cheaper, its used for faux enviromental reasons across the board.

You also mentioned nothing about the effect of using fuels with the incorrect octane ratings, at least not the correct reasons anyway.
 
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ubersonic said:
/Derp
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So what you are saying is, if you dont need to use high octane fuel, buy high octane fuel?

Hmmm.

What ARE you trying to say?

and what are the reasons for putting a different brand of high octane fuel in to your car when it doesnt need high octane fuel?

And why will your car go further on BP unleaded with its 5% ethanol content than it will on Tesco unleaded with its 5% ethanol content?
 
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atpbx said:
So what you are saying is, if you dont need to use high octane fuel, buy high octane fuel?
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No what I said was unless you really need 99 octane super unleaded (I don't think anyone does unless they have had their car remapped for it) then your better off with the 97RON super unleaded from BP/ESSO, I thought it was a pretty simple concept but I guess I should have made it more clearer >.>


atpbx said:
and what are the reasons for putting a different brand of high octane fuel in to your car when it doesnt need high octane fuel?
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Why would you put high octane fuel in your car if it doesn't need it? :confused:
 
ubersonic said:
Its complicated but basically when you buy normal/super from BP its 95/97 octane, when you buy it from somewhere like sainsburys its something like 93/95 octane mixed with an octane booster called ethanol to raise it to 95/97. Its cheaper than petrol of X grade but as ethanol has a lower calorific value than petrol (there's less energy in it) your car will not go as far on say Tesco unleaded as it would on BP unleaded. Tescos 99 sounds great but its 5% ethanol (the maximum allowed under EU law) so unless you really need 99 octane you would be better on BP/Esso super.
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The bit in bold, are you trying to say when BP and Sainsbury buy fuel wholesale from refineries it's at different octane ratings?
 
alx said:
The bit in bold, are you trying to say when BP and Sainsbury buy fuel wholesale from refineries it's at different octane ratings?
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/shrug I don't know the process involved, but if you took the ethanol out of Sainsburys fuel it would lower its octane rating, ethanol is ~109 RON.
 
Tesco fuel isn't the same as branded fuels. They were the first to add ethanol to their fuel and a few years ago one of the adatives they used ruined the lambda sensors on many cars. They had a huge repair bill from loads of cars.
 
Dandle said:
Tesco fuel isn't the same as branded fuels. They were the first to add ethanol to their fuel and a few years ago one of the adatives they used ruined the lambda sensors on many cars. They had a huge repair bill from loads of cars.
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Depends what you class as "isn't the same". They all come from the same refineries with the same minimum UK spec. All that varies is the additives they put in post production.
 
Well the update is the car has come out of the dealer with suspected contamination in the fuel tank. Obviously I can't say for sure if it is that particular fuel or station.

It has been flushed, fuelled up and reset. As it is still under a workmanship guarantee I am gonna run it really low and fill up there again and see if it happens again.
 
Third Opinion said:
Well the update is the car has come out of the dealer with suspected contamination in the fuel tank. Obviously I can't say for sure if it is that particular fuel or station.

It has been flushed, fuelled up and reset. As it is still under a workmanship guarantee I am gonna run it really low and fill up there again and see if it happens again.
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It's either your car or that particular station. How many focuses fill up every day trouble free?
 
Interesting observation I have made recently; I have almost always filled up at my local shell, but for convenience recently (moving house amongst other things) I have filled up at asda when I went shopping. This also coincides with me having a pair of part worn dunlops put on the front of the car (yes, yes, I know I know part worns blah blah blah the car is going before christmas all being well so whatever :p ).

I suddenly went from circa 420 miles for a tank down to around 360.

Attributing this to the new tyres, I had the tyres checked again by the tyre fitters, and also checked all pressures etc.

A few days ago I put in a full tank (from the fuel light) of shell petrol and today I hit 220 miles since refilling, and the gauge is showing slightly (1-2 degrees) over half, which is what I have always achieved up until a couple of weeks ago.

Could it be the case I am getting significantly less miles from a tank of asda unleaded than I am from shell unleaded? A circa 15% drop in economy is an awful lot in my eyes.
 
nout wrong with that asda petrol, I use it most of the time. As you know I log my fuel usage, and it's always 39mpg +/-1 despite many different brands of fuel.
 
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