Mercury - Quickleen Engine and Fuel System Cleaner Fuel Care System Liquid Formula 8M0058691. Overview. Anyone who's spent time on the water knows how quickly an engine's personality can change when carbon builds up or fuel quality slips. One day it's running smooth and confident, and the next it's hesitating, knocking, or feeling a little tired when you lean on the throttle. That's why having something you trust to keep the fuel system clean makes such a difference. Mercury Quickleen Engine and