Inboard? Outboard? Whatever floats your boat, Valvoline Full Synthetic 4-Stroke Marine Motor Oil is proven to maximize engine life. Unlike automobile engines, four-stroke marine motors face unique challenges from higher running speeds, seasonal use, and extreme operating environments that can lead to corrosion, excessive wear, and dirt deposits. Valvoline Full Synthetic 4-Stroke Marine Oil is optimized for performance and durability, providing 50% stronger wear protection and 8X better defense against rust than industry standards. All without compromising acceleration and horsepower. For peak performance, make sure your motor has the superior protection it demands. Full Synthetic 4-Stroke Marine Motor Oil from Valvoline – the trusted motor oil brand for more than 150 years.