Mercury - Premium Plus 2-Stroke Marine Engine Oil Synthetic Blend 858025K01. Overview. If you have spent enough time on the water, you know that trust in your engine isn't built overnight, it's earned. Mercury's Premium Plus 2-Stroke Marine Engine Oil is the kind of product that quietly earns that trust every time you turn the key. It's for the boater who knows what it feels like to run wide open across glassy water, who's felt the tug of the tide and the hum of a motor that just works. This oil