Mercury - Quicksilver Engine Coolant Temperature Gauge Sender For MerCruiser Sterndrives & Inboards 805218T. Overview. When you're out on the water, knowing your engine's temperature isn't just convenient - it's critical. The Mercury Marine 805218T Quicksilver Engine Coolant Temperature Gauge Sender gives you accurate, real-time temperature readings for your MerCruiser sterndrive or inboard engine. Designed and tested to Mercury's exacting standards, it provides dependable readings that help pre