Like I've said on another thread, my diesel Octavia, my previous diesel Picasso and my wife's petrol Megane all show a marked difference in performance and economy depending on where I last refuelled.

Branded name fuel such as Shell or Texaco = smooth tickover and running, and decent MPG. As soon as I fill will supermarket stuff,, lumpy tickover, noticiably more sluggish and definately thirstier. And the diesels seem to smoke more on supermarket fuel as well

Personally, now I won't fill up anywhere except Shell or Texaco, especally as my local Shell is actually exactly the same price as the Tesco within a half mile.

Hope this helps.

Mike

Do u fill up at Shell on Wigan Road?

I get £20 a quarter in Clubcard vouchers from filling up at Tesco... No way I'm changing!

80k on my Civic in 2.5 years now and the i-CDTi engine has been flawless.

Thats because it is Honda, quality mechanicals

Been driving diesels for as long as I've had my licence and I can honestly say that unless you get a bad batch of diesel the fuel makes very little difference as long as it complies to the EN590 standards.

I mean do you really think the supermarkets have their own refineries

I'd agree mostly. I did at one point get poor MPG on a couple of batches of Total from one garage, but overall, in 10 years of driving TDIs, I can't tell any difference.

I too would doubt there is any noticable difference between fuels. I always use Tesco (closest and cheapest) and can say I have never felt a difference when I have used Shell etc..

Also I would soubt you could accurately say it is 1-2mpg better as I see variations in my fuel economy of up to 6-7mpg depending on weather, traffic and even what music is on in car (though that more to do with the driving style that accompanies it!!!) on what is the same journey each day. So I can not see how anyone can reliably say they see 1-2mpg better economy with a particular fuel.

I believe there is some theory behind this that once we have made up a theory or belief then every one thing that supports that theory/belief needs around 10 or more things against it before we start to question it. Hence if you fill up with Tesco fuel one day, instead of say shell, and the conditions happen to give you poor mpg (i.e. heavy traffic or something) then you will assume it was the fuel but it would take another 10 times of filling at tescos and not seeing a change (or even seeing an improvement) before you would start to not believe the fuels were performing the same.

I also have friends in the refining business and they say similar things to the above, that is the base fuel is all the same it is just the additives that change.

Agree with the comment about petrol as opposed to diesel - higher octane stuff is less prone to detonate (knock/pink/whatever) under high compression and so is beneficial to tuned/high performance engines with low squish tolerances and high compression ratios. I have been riding performance bikes for the last 10 years and I have always filled them with 98+ RON petrol.

The Octavia on the other hand, gets whatever she is given, and runs just fine, thanks very much!!

If fuel is all the same and all comes from the same place, how did Tesco managed to ****-up, hundreds, possibly thousands of petrol cars a while back with contam'd petrol? :confused:

Can't speak for diesel but I would agree that usually petrol is much of a muchness and have alternated between shell and supermarket fuel. However I honestly believe I've had poor petrol on several occasions. I'm not sure how or why but I imagine it would be the distributor/retailer at fault rather than the supplier.

Anyone who thinks its makes a difference which brand fuel they put in are deluded. It is all pychosomatic and there is no difference that anyone here with a Skoda would ever be able to notice.

I have a Superb tdi, it was 130 bhp diesel, I revoed it so now it is probably 160bhp and if I drive normally you would hardly know the difference. Only when I boot it do I notice the difference in performance and smoothness.

Now this is an increase of more than 20% on power and people 'reckon' they know the difference between fuel qualities - Rubbish

Anyone who thinks its makes a difference which brand fuel they put in are deluded. It is all pychosomatic and there is no difference that anyone here with a Skoda would ever be able to notice.

I have a Superb tdi, it was 130 bhp diesel, I revoed it so now it is probably 160bhp and if I drive normally you would hardly know the difference. Only when I boot it do I notice the difference in performance and smoothness.

Now this is an increase of more than 20% on power and people 'reckon' they know the difference between fuel qualities - Rubbish

Question for you - have you ever driven somewhere on a cool, dark and slighty moist night, and thought your car was running exceptionally well that night?

I know what you mean, used to have an S4 and I could 'notice' the difference when it was foggy, but then again that might have been me brain tricking me and it is usually quieter on the road in those circumstance!

I think the science is that the air is denser, but God knows if that is true at all, but thinking it is is probably enough to make it true in my mind!

Having had a mammoth battle getting Tescos to help repair the (petrol) Corsa 1.4 16V that my wife used to have, after using Tesco's contaminated petrol, I'm sorry, but I'm sticking to my guns here, and not letting the Octavia anywhere near the pumps at supermarkets.

Exactly but how did it happen? :confused:

Was that Tesco thing not all from one site though? Might be my memory, but if it was all from one place then could be a contaminated tanker or storage unit at that particular site?The science of cool air is simple - colder air is more dense with oxygen for a given volume of air, so the charge going into the engine contains more oxygen molecules than air at a higher temperature. This makes the burn more complete, meaning each charge releases a little more power than it would do if the air were warmer.Follow the logic and you'll understand why altitude robs power (less oxygen at higher altitude) and turbos run intercoolers (re-create the effects of a cold night).Science lesson over - sorry to everyone who already knew that!!

So maybe it wasnt my imagination in the S4, never noticed it on the Superb though... Although the S4 was a twin turbod beast so it might have acutally made a difference!

:P

And did we ever find out exactly WHAT it was contaminated with??????????

On the Corsa, there were 11 of the 16 valves that NEEDED replacing, and we pushed for, and got, all 16 done whilst the engine was in bits.

Yes, it was well documented in the media. It was due to fuel sourced from a certain depot and I am surprised you don't know this being as you have been through the mill with it.

BBC NEWS | UK | Retailers offer car repair refund

It's worth pointing out that the company (Harvest) supply Shell, BP and a few other too. It just happened to be those tanks going to the Tesco/Morrisons forecourts. It could have been anyone really.

I think some prat put silicone into the tank of petrol by mistake. Silicone destroys the lamda sensor or does it no good thats what we were told by vauxhalls engineers when I was working at MSD.

Would also be interesting to subject the data that says supermarket fuel is worse to so simple statistics to see it there really is a difference in mpg between different suppliers.

As in work I will often think there has been an improvement but when you do some simple stats tests you realise it is just within normal variation.

I know what you mean, used to have an S4 and I could 'notice' the difference when it was foggy, but then again that might have been me brain tricking me and it is usually quieter on the road in those circumstance!

I think the science is that the air is denser, but God knows if that is true at all, but thinking it is is probably enough to make it true in my mind!

Here comes the science bit.

The air is denser, particularly when it gets to the cylinders, in those conditions. Reliable sources (like university educated automotive engineers) put the power gain at 1 or 2%. So the next question is, if you can notice a change of that magnitude, why shouldn't you notice the 5 to 10% that various people report (on basis of not changing driving style and getting improved fuel consumption) from different fuel?

Well based on how and where I drive, the difference was very noticable, especially with the PD100