“Does premium diesel work?”  Asked by a Google searcher, August 2012.

Most fuel brands offer ‘premium’ options for both petrol and diesel fuels.  They usually claim to give you more performance while using less fuel.  So how much gain do you get, and is it worth the price premium over regular petrol or diesel fuels?

What is premium unleaded petrol?

Premium unleaded petrol is usually a more refined form of petroleum than regular unleaded, with a higher octane number.  This makes it burn more efficiently, thus delivering more power for less fuel burned.  It may also have additives such as detergents to keep the inside of the engine clean.

The level of improvement you can expect to get from premium unleaded petrol will depend on your engine’s requirements, and your driving style and circumstances.  Some engines, usually in higher-performance cars, require premium unleaded anyway, and will suffer reduced performance and fuel economy if you use regular unleaded.  Some engines will see very little difference at all; if your driving is predominantly city commuting and school runs, you probably won’t notice any significant improvements.  If you tend to drive harder or do more open road driving, you may notice more substantial differences.

What is premium diesel?

Similarly, premium diesel fuel is usually a higher quality of fuel which burns more efficiently.  It may also have additives which help keep the engine clean and improve cold-temperature performance.

There is usually less difference in performance and economy between premium diesel and regular diesel than you get with premium unleaded petrol and regular unleaded for a single tankful.  However, premium diesel will potentially help your engine run smoother and cleaner, which can improve both performance and economy with regular use.  This may be more noticeable on older or higher-mileage engines than in a brand new car which hasn’t yet accumulated any sediments within the engine.

Try it and see

The best way to discover if premium diesel or premium unleaded petrol work for you and your car is to try about three tanks’ worth and see if you notice a significant and repeated difference.  If you can’t feel any improvement in performance and you don’t appear to be getting greater mileage from each tank, you’re probably better off sticking with regular petrol or diesel.  If you do notice improvements, you need to decide whether the increased cost (which can be up to 10p/litre) is justified.

Do you have a question for Stuart?

Ask your question below or e-mail Stuart at info @ TheCarExpert.co.uk now to have it answered in another edition of “Ask Stuart” very soon.

Recommended reading:

Are diesel cars suitable for city driving?:  How suitable are diesel cars for urban driving and short journeys?

Fuel economy: petrol or diesel?:  Should you buy a petrol or a diesel car?

Fuel economy: real-world vs. official figures:  Why is there always a large difference between the claimed economy figures and what you actually get?

fuel economy - premium petrol or premium diesel - the car expert

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Stuart Masson is the owner and editor of The Car Expert, a London-based website which provides expert and impartial advice for anyone buying a new or used car, as well as news and information from all over the automotive world.

This Post Has 9 Comments

  1. Angela

    Hi! I have been trying this for the last fortnight, and seem to be getting better mileage from premium petrol. I worked out that it’s costing me about the same, but I guess it’s probably worth it in terms of being better for my engine, isn’t it?

  2. Isaac @ Shell

    V-Power Diesel is a blend of regular petroleum-based diesel and synthetic diesel , created using gas to liquids (GTL), along with some extra additives designed to clean the injection system and improve injection pump and injector lubricity.

  3. Glenn Jamieson

    I think it’s all a con, and that it’s probably exactly the same fuel in the regular and premium pumps. Just an excuse for blood-sucking oil companies to screw us all over yet again.

  4. Adnan

    Hi Stuart,
    What happens if both premium and plain unleaded petrol is put into the tank? Say half premium and half plain? Will the engine explode? I am asking because I have a loose memory and will surely forget what I have put into the tank last time!

    Thanks,
    Adnan

    1. Stuart Masson

      Hi Adnan. For your car, it will make no difference at all. Your Toyota will run happily on regular unleaded petrol, although you may get slightly more power and/or better economy on premium unleaded. So you definitely don’t need to worry about it. If a certain engine is designed to run on premium unleaded, it will not run cleanly on regular unleaded and over time may misfire and develop problems. However, it is not going to cause the engine to explode or anything dramatic like that.

      Best wishes, stuart.

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