Mercury - Oil Pressure Gauge 0-150 PSI Dual Scale Black Face 2-1/8" (52 mm) 79-8M0069428. Overview. The Mercury Oil Pressure Gauge (79-8M0069428) gives you a clear picture of your engine's oil pressure so you can spot changes before they become problems. It reads up to 150 PSI and includes a dual-scale face showing both PSI and Bar, making it simple to read in either unit. The black face, bright white markings, and glass lens match Mercury's OEM styling for a sharp, factory look. It fits a stand