Mercury - Full Synthetic Marine Engine Oil 10W-30 4-Stroke Formula Premium Synthetic 8M0173223. Overview. Every boater knows that feeling when you push the throttle forward and the engine answers with smooth, confident power. That kind of trust doesn't happen by accident-it comes from taking care of the heart of your boat. Mercury 10W-30 Full Synthetic Marine Engine Oil (8M0173223) is the oil you reach for when you want absolute peace of mind, whether you're cruising across open water or easing