For motorists, any savings are welcome. And an obvious one is deciding whether or not to use the premium fuel that on many forecourts is now available alongside the regular offering.
What is premium fuel?
Many fuel brands such as Shell, BP and Esso offer a choice between regular petrol and diesel and a premium or ‘super’ version. These usually have sporty sounding names such as Nitro Plus or Ultimate and the implication is that they will boost the performance of your engine. They are more expensive than regular fuel, usually by around 10%.
What’s the science behind premium petrol?
All fuel has what’s called an octane rating or RON (it stands for Research Octane Number). This is particularly important for petrol engines. The higher petrol’s octane, the more it can be compressed in the engine’s cylinder before detonating. In basic terms, the more the fuel can be compressed, the bigger the bang and the better the performance. Regular fuels have a RON of 95. However, premium fuels are 97 or 98 RON.
Does your car need premium petrol?
You’ll be able to find out whether your car needs higher octane petrol by either looking on the petrol cap, inside the petrol flap or in the user manual. For most car owners, 95 RON is perfectly adequate; your engines will have been optimised to make the most of it and if you use 98 RON, you’re unlikely to notice any difference.
But if you have a performance car where the temperatures and compression are higher, then you may notice the engine runs more smoothly, particularly if you’re driving hard.
All fuel sold in the UK must conform to a European Standard for quality (EN228 for petrol, EN590 for diesel) so not buying premium fuel doesn’t mean you’re getting a substandard product.
Will premium petrol improve your car’s performance?
If your car has a 100 horsepower engine, that is its power output. Using a fuel with a higher octane rating won’t increase that output. It may increase its economy but the margins are likely to be so insignificant you won’t notice them. And the savings you’ll make on fuel won’t outweigh the extra outlay in cost.
What about premium diesel?
Diesel engines operate differently to petrol so rather than an octane rating, diesel has a cetane rating. This denotes how quickly the fuel burns in the combustion chamber (the faster it burns, the more efficient it is). The cetane rating between regular and premium fuels hardly varies.
Will premium diesel increase economy?
Where premium diesel differs is by having increased detergents and additives. These are designed to make the fuel burn more cleanly and minimise the build-up of deposits in the engine compared to regular diesel. As with premium petrol, they are unlikely to improve mpg significantly.
Independent tests by What Car? concluded: “Premium fuels are an unnecessary expense with no major fuel economy benefit.” Diesel Car magazine added: “Don’t spend money blindly on premium diesel if you can’t identify any measurable differences.”