Sierra Thermostat Gasket 18-0323 for Mercury Outboard Engines

The Sierra 18-0323 is a thermostat gasket engineered for Mercury outboard engines. It seats between the thermostat housing and the engine block or cylinder head, creating the seal that keeps the cooling system's water flow contained and prevents leaks at the thermostat housing joint. Over time, factory gaskets can compress, harden, or tear, which allows water to seep past the housing and can lead to overheating or coolant loss; replacing the gasket with the Sierra 18-0323 restores a tight seal at this connection point.

This is a small, single-use component intended to be installed whenever the thermostat housing is opened, whether for a thermostat replacement, inspection, or general cooling system maintenance on a Mercury outboard. Keeping a spare on hand is useful for any outboard owner who services their own cooling system, since the gasket should be replaced rather than reused each time the housing is removed.

Specifications

• Brand: Sierra
• Manufacturer Part Number: 18-0323
• Product Type: Thermostat Gasket
• Application: Mercury Outboard Engines
• Weight: 0.01 pounds
• UPC: 030999873125

Frequently Asked Questions

What is the Sierra 18-0323 used for? It is a thermostat gasket that seals the thermostat housing on Mercury outboard engines, preventing water from leaking past the housing joint.

Which engines does the Sierra 18-0323 fit? The Sierra 18-0323 thermostat gasket is designed for use on Mercury outboard engines.

Is the Sierra 18-0323 a genuine Sierra part? Yes, part number 18-0323 is manufactured and sold under the Sierra brand.

How much does the Sierra 18-0323 gasket weigh? The Sierra 18-0323 thermostat gasket weighs 0.01 pounds.

What comes in the package for the 18-0323? The Sierra 18-0323 is sold as a single thermostat gasket.

When should I replace the thermostat gasket on my Mercury outboard? Any time the thermostat housing on a Mercury outboard is removed, such as for a thermostat replacement or cooling system inspection, the gasket underneath it, like the Sierra 18-0323, should be replaced rather than reused since it will not reseal reliably once disturbed.

Can a worn thermostat gasket cause overheating? A compressed or torn thermostat housing gasket can allow water to leak past the seal, which can reduce cooling efficiency; the Sierra 18-0323 replaces that gasket to restore a proper seal.

What is the UPC for the Sierra 18-0323 gasket? The UPC for the Sierra 18-0323 thermostat gasket is 030999873125.