Mercury - Corrosion Guard Engine Protect Rust Inhibitor Spray 12 oz Can 80287855. Overview. Keep your engine looking new and running clean with Mercury Marine 80287855 Corrosion Guard Engine Protect. This 12 oz spray-on rust inhibitor forms a thin, water-resistant film that shields your outboard or sterndrive from corrosion without leaving sticky residue or buildup. Designed for use on engine blocks, under-cowl components, and exposed metal surfaces, it dries quickly and won't harm paint, rubber