Service centres recommend fresh oil every 10,000 km — a £90 ritual with a courtesy coffee and an upsell.
The self-administering alternative: a car with a slow, dignified leak performs a rolling oil change, continuously retiring the old fluid onto the driveway and inviting you to top up the new. Our researchers calculate the crossover point at 11 weeks, after which the savings become theoretical and the driveway becomes evidence. The engine, consulted, declined to comment.