Mercury - Quicksilver Water Shutter For Select MerCruiser Sterndrive Engines 807166A1. Overview. A small part with a big job, the Mercury Marine 807166A1 Quicksilver Water Shutter helps keep water where it belongs - out of your engine. Designed for select MerCruiser sterndrive and inboard engines, this shutter sits inside the exhaust system and acts like a one-way valve. When your engine is running, it allows exhaust gases to flow freely. When it's idling, off, or facing rough water, it swings s