Mercury - Oil Pressure Gauge 0-100 PSI Dual Scale White Face 2-1/8" (52 mm) 79-8M0052869. Overview. The Mercury Oil Pressure Gauge (79-8M0052869) gives you a clear, accurate reading of your engine's oil pressure so you can spot issues before they become problems. It features a dual-scale display showing both PSI and bar, making it easy to read in either English or Metric units. The white face, black numerals, and glass lens provide crisp visibility in all lighting, and it fits a standard 2-1/8"