Mercury - Oil Level Gauge Black Face 2-1/8" (52 mm) 79-8M0052852. Overview. The Mercury Oil Level Gauge (79-8M0052852) gives you a simple, reliable way to check your engine's oil level right from the dash. Featuring a black face, white markings, and a glass lens, it's easy to read in all lighting conditions and matches perfectly with the rest of Mercury's OEM gauge lineup. It fits a standard 2-1/8" (52 mm) hole and connects directly to SmartCraft systems equipped with compatible oil level sensor