Sierra 18-3675 Thermostat Gasket, Replaces Mercury 27-854961

The Sierra 18-3675 Thermostat Gasket is a replacement gasket engineered to seal the thermostat housing on applicable Mercury outboard engines. It creates the seal between the thermostat cover and the powerhead, preventing coolant leaks and ensuring the cooling system holds pressure correctly during operation. As a direct cross-reference for several Mercury Marine OEM part numbers, this gasket is built to match original factory dimensions and sealing surfaces, so it installs in place of the OEM part without modification.

Sierra manufactures its gaskets to meet or exceed the specifications of the original equipment they replace, giving boat owners and marine technicians a reliable option for routine thermostat service, cooling system maintenance, or full thermostat housing rebuilds. The gasket is compact and lightweight, shipping as a single unit ready to drop into place during a thermostat swap or cover reseal.

Specifications

• Brand: Sierra
• Manufacturer Part Number: 18-3675
• Product Type: Thermostat Gasket
• OEM Cross-Reference: 27-854961, 27-85496, 27-64204, 27-72508
• Color: Black
• UPC: 808282145262
• Weight: 0.01 pounds
• Package Height: 7.37 centimeters
• Package Length: 7.62 centimeters
• Package Width: 6.86 centimeters
• Country of Origin: China
• Unit Count: 1

Replaces (OEM)

• 27-854961
• 27-85496
• 27-64204
• 27-72508

Frequently Asked Questions

What is the Sierra 18-3675 used for? The Sierra 18-3675 is a thermostat gasket that seals the thermostat housing cover on the powerhead, sealing the cooling system so coolant does not leak past the cover during operation.

Which OEM part numbers does 18-3675 replace? It cross-references to Mercury Marine part numbers 27-854961, 27-85496, 27-64204, and 27-72508, so any of those OEM numbers can be replaced with Sierra 18-3675.

Is this a genuine Sierra part or an aftermarket copy? Sierra 18-3675 is a Sierra-manufactured replacement part, built to meet or exceed the specifications of the original equipment gasket it replaces.

How much does the 18-3675 gasket weigh? The Sierra 18-3675 thermostat gasket weighs 0.01 pounds.

What color is the Sierra 18-3675 gasket? It is black.

What is included when I order this part? Ordering Sierra 18-3675 gets you one thermostat gasket; the unit count for this listing is 1.

Where is the Sierra 18-3675 manufactured? The country of origin for the Sierra 18-3675 gasket is China.

Can I use 18-3675 for a thermostat replacement or housing rebuild? Yes, the gasket is intended for thermostat service and reseal work at the thermostat housing cover, including full thermostat replacement jobs.

What are the package dimensions of the 18-3675 gasket? The package measures 7.37 centimeters in height, 7.62 centimeters in length, and 6.86 centimeters in width.

Does Sierra 18-3675 come with a UPC for retail tracking? Yes, the UPC for Sierra 18-3675 is 808282145262.

Is the 18-3675 gasket reusable once removed? Gaskets are designed as a single-use seal; Sierra 18-3675 should be replaced with a new gasket any time the thermostat cover is removed to ensure a proper seal.