Sierra Thermostat Cover Gasket 18-0844, Replaces Yamaha 688-12414-A1-00

The Sierra 18-0844 is a thermostat cover gasket engineered to seal the thermostat housing on applicable Yamaha outboard engines. It forms the seal between the thermostat cover and the powerhead, preventing coolant leaks at this junction and ensuring the cooling system maintains proper pressure and flow around the thermostat. Sierra manufactures this gasket to meet or exceed the quality of the original equipment part it replaces, giving boat owners a reliable option when servicing the cooling system or replacing a worn or damaged gasket during a thermostat swap.

This gasket is a simple but essential wear item: over time, heat cycling and engine vibration can cause the original gasket material to harden, crack, or lose its seal, leading to coolant seepage around the thermostat cover. Replacing it whenever the thermostat cover is removed, such as during a thermostat replacement or cooling system inspection, is standard practice to avoid leaks after reassembly. The Sierra 18-0844 is sized and shaped to match the OEM thermostat cover gasket it replaces, so no modification is needed for installation.

Specifications

• Brand: Sierra
• Manufacturer Part Number: 18-0844
• Product Type: Thermostat Cover Gasket
• Weight: 0.01 pounds
• Quantity: 1 gasket
• UPC: 030999874771

Fitment

• Yamaha outboard engines using thermostat cover OEM part 688-12414-A1-00

Replaces (OEM)

• 688-12414-A1-00

Frequently Asked Questions

What does the Sierra 18-0844 gasket fit? The Sierra 18-0844 is a thermostat cover gasket for Yamaha outboard engines that use the OEM thermostat cover gasket 688-12414-A1-00.

Is the Sierra 18-0844 the same as the Yamaha OEM gasket? Yes, the Sierra 18-0844 replaces Yamaha OEM part 688-12414-A1-00 and is built to meet or exceed the original equipment part's quality.

How many gaskets are included with part 18-0844? One thermostat cover gasket is included per Sierra 18-0844 package.

What is the weight of the 18-0844 gasket? The 18-0844 thermostat cover gasket weighs 0.01 pounds.

When should this gasket be replaced? Replace the 18-0844 gasket any time the thermostat cover is removed, such as during a thermostat inspection or replacement, since the old gasket material can lose its seal after being disturbed.

What happens if a worn thermostat cover gasket is not replaced? A worn or hardened thermostat cover gasket can allow coolant to leak at the thermostat housing, so installing a fresh 18-0844 gasket during service helps prevent seepage.

Does the Sierra 18-0844 include the thermostat itself? No, the 18-0844 is the cover gasket only; it does not include the thermostat.

What material is the 18-0844 gasket made from? The 18-0844 thermostat cover gasket is made from OEM-equivalent gasket material to match the original Yamaha part.

Is Sierra 18-0844 genuine Yamaha or aftermarket? The 18-0844 is a Sierra-manufactured aftermarket gasket, made to meet or exceed the specifications of the original Yamaha equipment it replaces.

Can the 18-0844 gasket be reused after removal? Thermostat cover gaskets like the 18-0844 are designed for one-time installation; once removed, the seal is generally compromised and a new gasket should be installed.