Mercury - 10W-30 Marine Oil Four-Stroke Engine Lubrication 92-8M0078616. Overview. This quart of 10W-30 is a straightforward option for routine service on four-stroke marine engines. It's blended for how boats actually get used-long idle times, warm cruising, and plenty of moisture hanging around the powerhead. Fresh oil helps these motors settle into a smoother idle and run a little cleaner when you roll into the throttle. Nothing complicated about it, just a solid marine-grade oil that does it