Mercury - Water Pressure Gauge 0-30 PSI Cooling System Monitoring Black Face Black Bezel 79-8M6020031. OverviewThis 0-30 PSI water pressure gauge gives you a clear look at how well the cooling system is moving water through the engine. Out on the water, the needle settles into a smooth, steady sweep, so you can spot changes without squinting or guessing. It reacts naturally when you trim up, get on plane, or run through chop. It's one of those gauges that quickly becomes part of your routine gla