Sierra Thermostat Cover Gasket 18-2554-9, Replaces 27-41812, Fits MCM/MIE GM V-6 & V-8 Engines - Pack of 2

The Sierra 18-2554-9 Thermostat Cover Gasket seals the thermostat housing on MCM/MIE GM V-6 & V-8 marine engines, preventing coolant leaks at this common failure point. Each package contains two gaskets, giving boat owners a spare for the next service interval or enough material to service two engines in one job. This gasket is a direct fit replacement for the OEM thermostat cover gasket used on these engine families, restoring a proper seal without modification.

Installing a fresh thermostat cover gasket during any thermostat replacement, cooling system inspection, or routine maintenance helps prevent coolant seepage that can lead to overheating or corrosion around the housing. Because the part is sold in a pack of two, it supports both immediate repair needs and future maintenance planning.

Specifications

• Brand: Sierra
• Manufacturer Part Number: 18-2554-9
• Product Type: Thermostat Cover Gasket
• Package Quantity: 2 gaskets per pack
• Engine Fitment: MCM/MIE GM V-6 & V-8 engines
• Weight: 0.08 pounds
• OEM Cross Reference: 27-41812, 27-90556, 27-41812Q
• UPC: 808282162887

Fitment

• MCM/MIE GM V-6 & V-8 engines

Replaces (OEM)

• 27-41812
• 27-90556
• 27-41812Q

Frequently Asked Questions

What engines does the 18-2554-9 thermostat cover gasket fit? The Sierra 18-2554-9 is designed for MCM/MIE GM V-6 & V-8 marine engines.

How many gaskets come in a pack? Each 18-2554-9 package includes 2 thermostat cover gaskets, enough for a repair with a spare or for servicing two engines.

Which OEM part numbers does this gasket replace? It replaces OEM numbers 27-41812, 27-90556, and 27-41812Q on MCM/MIE GM V-6 & V-8 engines.

Is the Sierra 18-2554-9 a genuine OEM part or an aftermarket equivalent? It is an aftermarket gasket manufactured by Sierra to match the fit and function of the OEM thermostat cover gasket it replaces.

How much does the gasket weigh? The 18-2554-9 thermostat cover gasket weighs 0.08 pounds per pack.

When should I replace the thermostat cover gasket? Replace the 18-2554-9 gasket any time the thermostat cover is removed, such as during thermostat replacement or if coolant seepage is noticed at the housing.

Does this gasket fit both port and starboard engines? The 18-2554-9 is not side-specific; it fits MCM/MIE GM V-6 & V-8 engines generally, based on engine family rather than mounting side.

What is the difference between 18-2554-9 and 18-2555-9? 18-2554-9 is the thermostat gasket for GM V-6 & V-8 engines, while 18-2555-9 is a separate Sierra part number for 4-cylinder engine applications; make sure to order the number matching your engine.

Can I use one gasket from the pack and save the other? Yes, the 18-2554-9 is sold as a pack of 2, so one gasket can be installed now and the second kept as a spare for a future service.

What is included with the 18-2554-9 purchase? The package contains 2 Sierra thermostat cover gaskets; no thermostat or additional hardware is included.