Reminds me of my mother-in-laws neighbour many years ago. She had an Hilman Imp, and went in the petrol station for petrol on here way on holiday. She asks the attendant for Oil as she thinks it might need some being as she was going a long way. She thinks it might be better value if she buys 5 litres, or porbably a gallon in those days. Anyway to cut a long story short she filled the engine until it reached the filler neck, just about the whole 5 litres. You can imagine the mess it made...
True story..