Petrol - Supermarket vs. Branded

Crabman

But don't forget the fuel companies may be making a larger margin from selling to the supermarkets??

And I do remember a while back (mid 90's ) tesco advertised that they "add detergents" for "no extra cost". Wonder what happened to that argument... :think:

tomstickland

Ok, maybe not 9mpg, but a hot day (without aircon!) does make a difference to mpg, and a significant one.

I've just had a look in "Internal Combustion Engine Fundamentals" by J Heywood and in there he quotes the efficiency correction factor that auto engineers use to correct for air temperature. ie: if they do a test at 25 deg ambient temp, then can correct back to what they'd expect at 20 deg standard temperature.

The forumula is:
correction factor = sqrt(standard temp / measured temp) where the temperatures are relative to absolute zero (ie: add 273 Kelvin to the deg C values)

So, going from 30 deg C to 10 degC would make a difference of
sqrt (303/283) which is 1.034
ie: going from 10 deg to 30 deg makes approximately a 3.4% difference in engine efficiency. That would be 1mpg on a car that normally did 35mpg.

However, tyre drag, windows open and other anciallery loads will add a bit more, so a few mpg difference might be acceptable.


As to why manufactures don't make an cast iron claims, that's because of the nature of the situation. Fuels deteriote during storage, batches are distributed depending on supply and demand and each car is different. I expect the result to be that the mean difference is ever so slightly in favour of the big brands, but the spread of results is such that the two have a lot of cross over. ie: it's statistically likely that MrB might find that Tesco petrol he bought in December actually gave him more mpg than some Texaco he bought the previous week.

The fuel deteriation argument is very important - the Octane rating for Optimax is very weakly defined. People in the motorsport industry have found that Optimax loses its Octane rating very quickly during storage.

Octane rating will affect efficieny on most modern cars since they automatically advance the spark timing if the fuel will allow it. Retarding the timing off optimum will cause a few percent lose in torque output.

There is also the business aspect of it. If Shell produce petrol for Tesco and then run a campaign stating that their fuel is 2% more efficient than Tescos then Tesco might not like that very much.

I've just found this on another forum.
Take with your own pinch of salt.

I work with petrol companies, so i'll let you into some lesser known secrets.

Super unleaded is a fine fuel, but only if purchased from reputable dealers. Esso SUPER, like BP are about the best you can buy. Supermarket stuff is just 4 star without the valve addictive, which itself is just 95 unleaded that has been octane boosted. AVOID AT ALL COSTS. Supermarket petrol is a very dirty fuel. Any engineer of their pumps will confirm that.
I have seen the results of their filters and you get everything from feathers to god knows what flowing through supermarket fuels. EVEN SAND.

All Super by law has to be 97 ron, but where its stable enough to hold higher octane, stations are able to advertise its octane as being higher sometimes.

Optimax has a variable octane rating, due to its structure its less stable, but leaves the refinery at 101 octiane.
Thats the equivalent to the old 5 star for those old enough to remember it.
By the time you buy it, its closer to around 97.
This is why its octane isnt always stated.

Normal 95 or 97 fuels wont lose octane, whereas optimax does, but used fresh, its the highest octane fuel you can buy.

Originally Posted by astramod
All supermarket fuels come from either the Matex or Purfleit refineries for the south east. These only take oil from the eastern block. They are most definately NOT the same fuels as ESSO and such like.
They also remix contaminations for other companies then sell the fuel on via supermarkets as well.
On average, each 50 litres brought from a supermarket will have 8% contaminates, and 9 grams of grit.
I have got 2 test tubes sitting on my desk at work of both ESSO and Tesco regular 95 for simple comparisons when arguing these points with supermarket buyers.
There is a bead in both which on the Tesco tube floats in mid suspension due to the grittiness of its petrol.
The ESSO falls straight to the bottom.
These are random samples taken every few weeks, and the results are always the same.

Texaco is a subsidary of ESSO and both use the same petrol.

There are basically 3 companies which supply fuel to the UK. ESSO, BP, AND SHELL.

Each sells to all the other names you find.

JET, FINA, Q8 and a few other smaller outlets all use SHELL.

TEXACO and TOTAL use ESSO,

Supermarkets use Eastern Block fuels, which are primarily designed for the 91 Ron continent market.
These are upgraded in the UK to UK specs by using Butane gas.
Hence to avoid.

BP Ultimate is just its old Super grade cleaned up a bit.
IE. It goes through another filter at the refinery.
Not a bad fuel though, second only to ESSO in quality.
Its Diesel is the best in the world for all you Diesel owners.

OPTICRAP. Need i say more. All grades supplied by Shell.
Might as well fill from your local FINA station and pop a bottle of Halfarts octane super duper booster plus in.

ESSO 95 and 97 = If you want every pennies worth in quality petrol, look no further.
Get it at your local TOTAL, TEXACO or ESSO now

http://www.migweb.co.uk/forums/vauxhall/car-talk/171266-asda-petrol-76-9p.html?highlight=fuel

tomstickland

Some questions asked about the validity/reliability of that previous quote.
Anyway, more stuff:

This months ride magazine (bike mag) has done a feature on fuels.

Ride is renowned for being the best in the business for testing stuff out fairly and being honest with the results. its a biking bible.

It goins into a lot more detail, but ill briefly post the results.

Cost:
standard fuel 100%
Optimax - 5.8% more
Ultimate - 7% more

Suzuki GSXR600 (Fuel injected)
Standard 98.5 bhp
Optimax 100.4 bhp
Ultimate 100 bhp

Kwak ZX6R (Carbs)
Standard 101.8 bhp
Optimax - 102.7 bhp
Ultimate - 102.9 bhp

Fuel was bought at a busy garage to ensure supplies were fresh, and engines were on the dyno 5 times for each fuel, drained, flushed and then run for 20 miles between fuel to ensure no crossover.

They finish by saying 'you can expect a power gain authough it was hard to spot on the road'
They measure a cost of 7% over an increse of only 2%.
They also mention slightly better mpg.

northern_munky

Going back to the temperature thing, you may see a rise in MPG when its warm because the engine oil is going to be very thin which equals less friction on all the moving parts inside the engine. Engines are actually more efficient when the air going in is cold, the air is much denser, thats why most cars with turbo chargers have intercoolers.

snapdragon69

How can anyone who purports to be a 'money saver' fall for all this advertising nonsense.

I used to work for one of the fuel companies at a depot.
Here is some of what I learned....

The fuel comes from any one oil company's refinery to the terminal (usually by pipeline, at some by train), and not only may that refinery supply it's own depots, it often supplies several other oil company's depots which are often located in clusters of 2 or 3 adjascent depots.

Now the fuel is stored in those large storage tanks at these depots (as at Buncefield) as raw product, the additive is a very concentrated liquid added as the tanker is loaded with the fuel. Note that the additive is not itself a fuel, it doesn't have any appreciable energy value and is added in tiny quantities.

Well, what happens to the fuel at this depot? Well, it is sent out to petrol stations not only by the oil company to their own stations and customers, but also to other oil company's stations who don't have a depot in that area and to supermarkets, it is delivered in unmarked tankers owned by Hoyers, P&O, Wincantons etc...

So, are they delivering the same stuff? Well, the raw fuel is exactly the same, the additives are usually the same, but sometimes in different quantities, and sometimes the other oil companies insist on their own additive being used, for example, Texaco Clean System 3.

Don't forget, all fuels sold meet the EN (Euro Norm) dictated by the EU, anything else you get, is over and above what the EU, vehicle manufacturers and fuel companies agreed is a minimum standard.

snapdragon69

tomstickland, whoever that is that you are quoting on some other forum needs locking up! Some saddo with compulsive obsessive fuel disorder, grit! :rotfl: . Texaco owned by Esso LMAO,:rotfl:
Esso is owned by Exxon Mobil, Texaco is owned by Chevro. Has he never heard of the company TotalElfFina?
Probably a 12 year old troll.:T

tomstickland

Yes, he might well be, I did say "with pinch of salt".

How can anyone who purports to be a 'money saver' fall for all this advertising nonsense.

What advertising nonsense? We're talking about big name 95 premium versus supermarket 95 premium.
Plenty of people claim that they have seen a difference in favour of big name, noone has seen the opposite. I think the difference would be very small, but there might be a difference.

As to super unleaded, the higher Octane rating will provide more power and/or better fuel economy on some engines. Not enough to justify the higher price though.

As to additives, you can buy Octane boosting chemicals from motor factors and these do work. So you can convert cheapo 95 RON to higher RON by adding a very small quantity to tank of fuel.

tomstickland

Edit: large dose of salt.
i have found some good info via the Dishonest John website

If I can summarise this correctly, the position is believed to be that all fuel meets a minimum British Standard. Fuel comes in bulk from various refineries, none of which are owned by supermarkets SFAIK. The difference, where if is one, is down to the quantity and quality of the additives which are added to the fuel, at the point of delivery, by the tanker drivers. So, all the fuel is good enough to meet the minimum legal standards and then is or is not improved, depending on what you believe, by the addition of additives which increase the price and may or may not improve performance, engine cleanliness, and mpg.

GabbaGabbaHey

Evo magazine has also done testing on various petrols and they found that Shell Optimax (now reformulated as V-Power, and 99 rather than 98 octane) was the best, with BP Ultimate also doing well. I think they used a BMW M5 and a Subaru Impreza Turbo as the test cars.

They did reasonably scientific testing (drained tanks, using dynos to measure power, etc), but they also made the point that the freshness of the petrol had a significant effect, and that you should always buy from a garage with a high turnover.

Personally, it's only in an emergency that I would put anything other than Optimax/V-Power in my cars.

tomstickland

Evo would have been interested in power output mainly, though more power does suggest better efficiency too.

My opinion from what I've read today is that additives are the only difference, and it is plausible that some of these might make a small difference to mpg.

From a MSE point of view, it'd be interesting to see whether adding your own additives is cheaper than paying for a garage to do it.