When it comes to optimizing the cooling system of high-performance Mercury Racing outboard engines, two critical OEM components ensure reliable performance: the Mercury restrictor washer (Part #12-47533 1) and the thermostat water outlet seal (Part #27-62386).
 
These parts work together to regulate water flow and maintain optimal engine temperature, which is essential for peak power output and engine longevity. The Small Restrictor Washer (0.123" / 3.12 mm ID) is engineered for high water pressure applications, delivering maximum cooling and high-flow performance—ideal for factory race setups (PN: 475331).
 
The restrictor washer helps manage coolant flow within the cooling system, especially under high-speed or racing conditions. By limiting excessive coolant bypass, it helps the engine reach and maintain its ideal operating temperature, avoiding both overheating and overcooling.
 
Proper temperature regulation enhances combustion efficiency and overall engine responsiveness—crucial in high-performance marine environments.
 
Meanwhile, the thermostat water outlet seal (27-62386) ensures a secure, leak-free seal around the thermostat housing. This maintains consistent water pressure, preventing coolant leaks that could reduce engine performance or lead to overheating.
 
Both components are manufactured from durable, marine-grade materials that meet or exceed OEM Mercury Racing standards, ensuring long-lasting performance in extreme conditions. Their direct-fit design allows for easy replacement with no modifications, making them a trusted choice for mechanics, racers, and marine performance shops.
 
To support professional builders, technicians, and dealers, Buckshot Racing #77 offers a convenient 20-piece dealer pack includes 10 x OEM Mercury restrictor washers (12-47533 1) and 10 x OEM thermostat water outlet seals (27-62386)
 
This bundle is ideal for high-volume users such as marine dealers, race teams, and performance-tuning shops. Buying in bulk not only ensures you're always stocked but also reduces the cost per unit.
 
Both the restrictor washer and outlet seal are compatible with Mercury Racing and Mercury Marine high-performance outboards and sterndrive engines, and fit seamlessly with billet water outlet kits featured on this site.
 
Applications include: Offshore racing boats, High-performance recreational boats, Modified cooling systems on custom speedboats, F1 Tunnel Boats, Mod VP and Outboard Drag Racing.
 
Proper cooling is key to unlocking consistent power and long engine life in Mercury Racing engines. The OEM 12-47533 1 restrictor washer and 27-62386 thermostat outlet seal are the smallest factory-approved size for high-pressure cooling setups.
 
Whether you're upgrading or replacing components, trust genuine Mercury Racing OEM parts for unmatched performance, fit, and reliability in the most demanding marine environment
 
Contact Mike at 714-697-1716 or mike@buckshotracing77.com for technical support.