Sierra 10W-30 4-Stroke Synthetic Marine Oil Sierra 10W-30 Synthetic Blend Engine Oil is formulated specifically for 4-stroke outboard and sterndrive engine technology. The special blend of synthetic base oil and a balanced additive system exceeds FC-W requirements and provides excellent protection at high temperatures. This superior protection works under heavy engine loads and offers faster lubrication at start up. Note Do NOT mix with gas - NOT for use in 2 cycle premix or injection engines. F