Mercury - Quicksilver 5W-30 4-Stroke Full Synthetic Marine Engine Oil Premium Marine Lubrication Full Synthetic Protection 8M0148475. Overview. If you've spent enough time on the water, you know how much trust you place in your engine every time you turn the key. It has to fire up cleanly, push through chop, idle smoothly through no-wake zones and take you home without hesitation. The oil inside it plays a bigger role than most people realize, quietly protecting everything that keeps you moving.