Improved Quicksilver® 25W40 4-Stroke Marine Engine Oil outperforms automotive oils in marine applications because of its specialized additive package designed for sterndrive and outboard marine engines. Quicksilver 25W40 4-Stroke Marine Engine Oil also boats approval for use in all outboard engines; previously only the synthetic blends could make this claim. You'll get flagship engine and corrosion protection—industry-leading strength and viscocity retention and ultimate corrosion and wear protection. This high-performance Quicksilver boat oil even exceeds all marine-industry 4-stroke oil requirements, including FC-W and FC-W Catalyst Compatible. Outperforms car oils with its specialized additive package just for boat engines. Industry-leading strength and viscosity retention. Ultimate corrosion and wear protection. Exceeds all marine-industry 4-stroke oil requirements.