For as long as I can remember – from way before I was a driving instructor – I have repeatedly heard the old story trotted out about how supermarket fuel is of inferior quality and can damage your engine. I even got it from an Esso cashier a few years ago when I told him I could fill up at Asda for up to 10p per litre less than what the Esso garage had just hiked its prices to.
Before I go into any detail, let me just say that that claim is a load of bollocks, and is perpetuated by people who don’t have a clue.
All fuel sold in the UK must conform to EN228 or EN590 (petrol and diesel, respectively), and unless you have a car which states otherwise in the manual, it will run comfortably on fuel which meets these specifications. The only difference is that some major garages may include extra additives designed to improve performance of their basic “premium” grade (and note that I said “may”). The “super” grades definitely contain additives, along with that other “additive” of about 10p per litre on top of the forecourt displayed price. EN228 and EN590 ensure that any fuel does not damage your car, and they also ensure that you don’t get the famous “residues that gunk up your engine” crap that people love to tell you about. You can read more about it here.
There is no way that the majority of driving instructors fill up with “super”. They use regular “premium” like the rest of us. If I used “super”, my fuel bill would increase by about £500 a year.
When I drove a petrol Ford Focus, the handbook told me I needed to use a minimum of 95 RON fuel. “RON” is the Research Octane Number, and the larger the RON number, the more expensive the fuel. Normal “premium” petrol is the bog-standard grade, and is 95 RON. The higher grade 97/98 RON is the “super” type, and often has an amusing comic book name like “Super-X Excelleratium Ultra Hyper-Q Unleaded Fuel”, alongside some graphic likely to appeal to chimpanzees in fast cars. Higher performance cars tend to specify 97/98 RON as a minimum, but normal cars don’t. Unless your handbook specifically tells you to use higher than 95 RON, you will have no trouble with it. I never did.
A similar thing applies to diesel fuel. The big garages may have a “super” grade alongside the basic one, but smaller garages don’t. For the last 5 years or so, I have exclusively used Asda for my diesel fuel. I have had no engine problems, and I get excellent mileage (over 50mpg).
In 2010, while I was still driving petrol cars, I had a problem with erratic idling on my Focus (across several cars, I should add). Even the dealer tried to argue that it was down to the fuel, and advised me to use “super” and give the car a “good blow out” on the motorway. It was absolute bollocks – the pre-2013 model cars all had the same fault, and a mechanical fix was needed. But if the dealer trotted out that same crap to other owners, the myth would just get perpetuated for another generation.
Supermarket tankers fill up from the same places the bigger garages do. Sometimes, you’ll even see one of the “bigger garage” tankers delivering to a supermarket. But it all meets the EN228 and EN590 specifications.
As an additional tip, I fill up at Asda – where the fuel is always about 5p cheaper than the local garages to start with. I use an Asda Cashback+ credit card, which gives 2% cashback on all Asda purchases (including fuel), and 0.2% on all other purchases. I pay it off before any interest is charged, and since I shop at Asda anyway – spending upwards of £150 on groceries most weeks, and over £100 on fuel – cashback soon mounts up. I know 2% doesn’t sound a lot, but it is the equivalent of about 3p per litre of fuel, so if Asda is charging £1.32, I end up paying £1.29. I save at least £150 a year just based on fuel purchases, and at least double that on everything else.