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Is it worthwhile using premium fuel in an engine that doesn't need it?

A few years ago, the word was that using BP 98 ULP in a vehicle that only needed 91 would rejuvenate and clean the engine and give better economy. I tried it in my 2020 Subaru Forester on a 2500km road trip and was happy with the fuel use; about 6.0 litres per 100km. Is this peculiar to BP fuel or are other mainstream 98 fuel suppliers just as good? Or am I wasting my money compared with filling up with 91 every time? Is it worth the extra 20 cents (eight to 10 per cent) compared to 91 for day-to-day driving?

The short answer is no, the extra cost is not justified in a vehicle that does not require premium unleaded. While some premium fuel products do contain detergents to help keep an engine internally clean (which is the basis of the claim you heard) the major difference (and the reason PULP costs more) is to do with the octane rating of the fuel.

Put simply, engines in a higher state of tune require this higher octane rating to produce their potential and well as avoiding internal damage. Your Subaru, meanwhile, is tuned to be quite happy on standard 91 RON ULP, and filling it with the more expensive premium brew is a waste of money. You might gain a small improvement in performance and/or economy, but not enough to offset the higher per-litre price of PULP, and probably not enough to even notice.

Disclaimer: You acknowledge and agree that all answers are provided as a general guide only and should not be relied upon as bespoke advice. Carsguide is not liable for the accuracy of any information provided in the answers.


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