Mercury - Mercury Racing 25W-50 4-Stroke High Performance Marine Engine Oil Racing Series Synthetic Blend 25W-50 8M0078013. Overview. There's a different kind of energy that comes with running a performance engine. The throttle feels livelier, the boat responds quicker, and every sound coming from the transom carries a little more excitement. But with that excitement comes heat, load, and hours of steady high-revolutions-per-minute running that demand more from your oil than everyday cruising ev