Sierra 18-3631 Thermostat with Housing, Replaces Mercury 892864T04, Fits 135-300 Verado

The Sierra 18-3631 is a complete thermostat and housing assembly built for Mercury outboard engines, designed as a direct replacement for the original Mercury 892864T04 unit. This assembly combines the thermostat element and its mounting housing into a single part, simplifying cooling system service by eliminating the need to source the thermostat and housing separately. It is intended for the Mercury 135-300 Verado engine lineup, where maintaining correct operating temperature is critical for engine longevity and performance.

The thermostat regulates coolant flow through the engine block, opening and closing at the designed temperature threshold to keep the engine within its proper operating range. A worn, stuck, or failing thermostat can cause overheating or inefficient warm-up, so replacing this assembly at the first sign of temperature irregularity helps protect the powerhead from heat-related damage. Because the housing is included, installers do not need to reuse or inspect an old housing that may have its own wear or sealing issues.

Sierra manufactures this part to meet or exceed the specifications of the original equipment it replaces, and it is built to hold up in the marine environment. The assembly ships as a single unit ready for installation, weighing 0.5 pounds.

Specifications

• Brand: Sierra
• Manufacturer Part Number: 18-3631
• Product Name: Thermostat with Housing
• Weight: 0.5 pounds
• UPC: 808282360924
• Unit Count: 1
• Fitment: Mercury 135-300 Verado

Fitment

• Mercury 135-300 Verado

Replaces (OEM)

• Mercury 892864T04

Frequently Asked Questions

What does the Sierra 18-3631 thermostat with housing fit? The Sierra 18-3631 fits Mercury 135-300 Verado outboard engines.

Does the 18-3631 replace the Mercury 892864T04 thermostat? Yes, the Sierra 18-3631 is a direct replacement for the Mercury 892864T04 thermostat with housing.

Is the housing included with the Sierra 18-3631, or just the thermostat element? The 18-3631 includes both the thermostat and its mounting housing as one complete assembly, so no separate housing purchase is needed.

How much does the Sierra 18-3631 thermostat assembly weigh? It weighs 0.5 pounds as a complete thermostat and housing unit.

Is Sierra 18-3631 a genuine Mercury part or an aftermarket replacement? The 18-3631 is a Sierra-manufactured aftermarket assembly engineered to replace the Mercury 892864T04 thermostat and housing, built to meet or exceed the original part's specifications.

What is included in the box with part number 18-3631? The package includes one complete thermostat with housing assembly, part number 18-3631, ready for installation.

What is the UPC for the Sierra 18-3631 thermostat with housing? The UPC for the Sierra 18-3631 is 808282360924.

Why would I need to replace the thermostat and housing on a Mercury Verado engine? A worn or stuck thermostat can cause overheating or poor warm-up on Mercury 135-300 Verado engines, and replacing the 18-3631 assembly addresses both the thermostat and its housing at once.

Can the Sierra 18-3631 be used on other Mercury engine models besides the Verado? The 18-3631 is specified to fit Mercury 135-300 Verado engines; fitment outside that range is not stated.

How many thermostat units come in one Sierra 18-3631 package? One complete thermostat with housing unit is included per package of the 18-3631.