19300-ZVT-003 Thermostat Assembly - Overview. The 19300-ZVT-003 Thermostat Assembly is a critical component of Honda marine engine cooling systems. This assembly regulates the engine temperature by controlling the flow of coolant, preventing overheating, and helping the engine maintain its optimal operating temperature. Designed to exact factory specifications, it fits seamlessly with existing engine hardware and promotes the reliable functionality of Honda marine engines.. Key Features. Genuine