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Dear advisor, I’ve been told that using a full tank of high-octane petrol yearly cleans the pistons and catalytic converter. Does this work? Please advise.

Hi there,
I've not heard that one before, sounds like a magic brew to me!
Some fuels have additives that claim to aid in cleaning the inside an engine. But in reality it would be more beneficial to run good oil, change it annually, keep the air filter clean and carry out regular trips which can clean out any carbon build-up from round town driving.