Mercury - Quicksilver Water Temperature Switch Engine Monitoring Part For Audio Warning Systems 48952. Overview. When your engine starts running hot, every second counts. The Mercury Marine 48952 Quicksilver Water Temperature Switch is the part that sounds the alarm before heat does any damage. It's made for MerCruiser sterndrives and inboard engines with built-in audio warning systems, turning on the buzzer when the temperature rises past safe limits. Built tough with marine-grade materials, it