Mercury - Quicksilver Thermostat O-Ring Gasket For MerCruiser 4.5L & 6.2L Engines 806871Q. Overview. A proper seal around your thermostat means steady cooling and reliable performance. The Mercury Marine 806871Q Quicksilver Thermostat O-Ring Gasket is designed for V6 and V8 MerCruiser sterndrive and inboard engines with the newer 1-piece thermostat housing. It's also used on 4.5L and 6.2L MPI engines (serial number 2A456613 and up). Made from high-quality, heat-resistant rubber, this O-ring crea