Mercury - Quickleen Engine & Fuel System Cleaner Fuel System Care Liquid Formula 8M0047921. Overview. There's a certain calm that comes from hearing your engine settle into a smooth, confident idle the kind that tells you the fuel system is clean and breathing easily. If you spend enough time on the water, you know how quickly carbon can build up and steal that effortless performance. Quickleen brings that clean-running feeling back. With just a little added at each fill-up, you'll notice your e