Mercury - Quicksilver 25W-40 4-Stroke Marine Engine Oil, 1 Quart Marine Engine Oil Standard Finish 8M0078619. Overview. There's something comforting about knowing your engine is running on clean, trusted oil - that steady hum, that smooth throttle response, that quiet confidence as you head out from the dock. When you spend your weekends on the water, you start to appreciate the small things that keep every trip easy and trouble-free. Quicksilver 25W-40 4-Stroke Marine Engine Oil, part number 8M