Mercury - Replacement Thermostat OptiMax 3.0L & V6 Series Marine-Grade Brass & Stainless Components 8M0057307. Overview. There's a certain comfort in knowing your engine is running at the exact temperature it was designed for. When you're cruising across open water or easing into a quiet cove, you want to feel that smooth, steady power beneath you-no hesitation, no surprises. The Quicksilver 8M0057307 130-Degree Fahrenheit Thermostat helps keep that feeling consistent. It maintains the cooling s