Supermarket petrol

[cromwell]

Around here supermarkets sell the cheapest petrol. But, i don't seem to get the mileage out of it. If I buy BP or Total, I always seem to get better mileage. So I can't see much of an advantage in buying cheaper petrol if you don't go as far on it.
It's passing strange because all petrol is supposed to have the same RoN rating, either 95 or 97, but it doesn't seem to be like that in practice.
Does anyone else find this?

[Workingman]

When I used to drive to the S of France for holidays I always put the same number of litres in at every fill up. The distance travelled always varied by quite some way even taking terrain into account. I had always thought that it was to do with the other chemicals added - different mixes from different companies - to the raw fuel.

One thing I do remember is that not all litres are equal. A litre is a volume, and how much "stuff" there is in a set volume is subject to temperature. Warmer fuel has fewer "bang" atoms than cooler fuel, so always top up in the late evening. A 1% or 2% difference to a full tank can be quite a few miles.

Fuel should be sold in kilograms so that we always get the same amount.

[meriad]

A while back there was a discussion about petrol on the cat forum and one of the members that posts is a Senior Consultant for Engine and Vehicle Testing for Shell and she replied:

OK why buy a branded product. Firstly Morrisons or Tesco fuel should not do any damage to your car in any way. Why? Becuase they buy their fuel from a BP, Shell or Essar refinery, which sells them a top quality base product. The big difference is in the additives that Shell, BP, Texaco, etc put in to (a) protect your engine for the long run (b) keep it clear of soot and deposits which could cause a loss of efficiency, resulting in consuming more fuel and (c) in producing better combustion which inturn makes the engine (gasoline or diesel) work much better.

Shell spend over £50M per year on research into our fuel and lubricant products for the global market. Our products really are proven to give fuel efficiency and performance benefits for the lifetime (150,000 miles) of the engine and after-treatment devices. We begin testing a product at least 3 years befores it hits the market. First we test to ensure it won't harm the vehicle, the environment or people over 150,000 miles of life of the vehicle. We use accelerated test methods, the last part of this is on public roads using real life driving. Unfortunately the very last step is to prove our products meet emissions and fuel economy legislative limits globally and for this we have to use standard test methods which often don't reflect real life, but they do give us a benchmark against what our competitors can offer.

I admit to not always using our own products as I fill up with whatever is closest, however, it will always be a Shell, Texaco, BP or Esso product as I know what goes into them is designed to clean and protect my vehicle for life. Supermarket fuels have cheap additive packs in them which are mainly designed only to clean the engine not to protect it for life.

I hope this helps clarify the situation for everyone and let you know why our fuels cost that bit extra.

Since she posted that I have tried where possible to fill up with a branded petrol and I do think that I get just that bit more mileage out of it

[Workingman]

Ria, I am so glad you posted that. I was beginning to think people had me down as a nutter for mentioning the additives the main companies add to the fuel. I knew that it was true because when I was in the RAF some people would "borrow" military fuel and it would make their cars 'pink' meaning that the ignition timing had to be altered. The fuel was two star rated, but in the raw state - without additives.

BTW aircraft get their fuel by weight, not gallons or litres, because of the other thing I mentioned. Another truth.

[cromwell]

Thanks Ria, that's very informative. So, there is some truth in it after all.