Mercury - Water Pressure Gauge 0-30 PSI Cooling System Monitoring Black Face Brushed Bezel 79-8M6020043. OverviewThis 0-30 PSI water pressure gauge gives you a straightforward feel for how well the engine's pulling water through the cooling system. The needle moves in a smooth, relaxed way, so you can spot changes without guessing. Out on the water, it reacts the way you expect-whether you're getting on plane, trimming up, or running a skinny stretch. It's a simple, dependable gauge that helps y