Yamalube 4M is a mineral-based four-stroke outboard engine oil that's an approved NMMA FC-W formulation specifically for use in the harsh marine environment. The FC-W rating, which sets the minimum standard for outboard engine lubrication, corrosion protection, and resistance to potentially harmful effects of oil dilution caused by fuel, provides critical assurance that your outboard's oil meets the minimum. Yamahas exclusive and proprietary additive package means Yamalube 4M meets or exceeds the industry standards for lubricity and corrosion protection. Automotive engine oil will not pass the rigors of the FC-W test. In fact, most automotive engines cruise at 2500 rpm, whereas an outboard can typically operate from 4500 to 6000 rpm all day long. That kind of stress will literally tear automotive engine oils apart. Simply put, an automotive oil is not designed or formulated to provide the protection required by an outboards moisture-rich, high-rpm, high-load environment.