Mercury - Water Pressure Gauge 0-30 PSI Cooling System Monitoring White Face Chrome Bezel 79-8M6020019. OverviewThis 0-30 PSI water-pressure gauge gives you a clear, steady read on how well the engine is pulling water through the cooling system. The needle settles with a smooth, even swing, so real changes stand out without getting lost in bumps or chop. Out on the water, it turns into a quick habit-glance, confirm, and keep moving. It's a simple, clean gauge that helps you stay ahead of cooling