Mercury - Quicksilver 4-Stroke 25W-40 Synthetic Blend Marine Oil (Quart, 6-Pack) Engine Lubrication 92-8M0078622. Overview. This oil is the blend most techs reach for when they want something steady and predictable in a 4-stroke outboard. It holds its weight well through long idle stretches, warm runs, and the stop-and-go rhythm a lot of boaters put their engines through. Pouring it in, you can feel it has the right body for marine use-not too thin, not sluggish. It's a straightforward choice th