Sierra Thermostat Kit 18-3647 - 160F Thermostat for 1987 & Newer GM Engines with Standard Cooling

The Sierra 18-3647 Thermostat Kit is a complete replacement kit built for 1987 and newer GM engines that require a 160 degree F thermostat with a standard cooling setup. Rather than sourcing a thermostat and gaskets separately, this kit bundles every component needed for a single, complete cooling system service in one box, reducing the chance of a mismatched gasket or a missed part during reassembly.

The kit includes a 160 degree F thermostat along with matching cover gaskets, housing gaskets, and an O-ring, so the full sealing surface of the thermostat housing can be renewed at the same time as the thermostat itself. This is important on marine engines, where a worn gasket or hardened O-ring is often the actual source of a coolant leak even when the thermostat is replaced on its own. Each component in the kit is manufactured to meet or exceed the specification of the original equipment part it replaces, making it suitable for routine maintenance or as part of a cooling system troubleshooting repair.

Because the thermostat is rated for standard (non-closed) cooling systems, confirm your engine uses standard cooling and requires a 160 degree F thermostat before ordering, since raw water and closed cooling setups commonly call for different temperature ratings.

Specifications

• Brand: Sierra
• Manufacturer Part Number: 18-3647
• Product Type: Thermostat Kit
• Thermostat Temperature Rating: 160 degrees F
• Cooling System Type: Standard cooling
• Weight: 0.32 pounds
• Product Dimensions: 5 x 5 x 3 inches
• Category: Mercruiser Thermostats & Gaskets
• UPC: 808282101213
• Kit Contents: 1x 18-2552 Thermostat Cover Gasket, 1x 18-2553 Thermostat Gasket, 1x 18-2844 Thermostat Cover Gasket, 1x 18-2917 Thermostat Housing Gasket, 1x 18-3649 Thermostat, 1x 18-7173 O-Ring, 1x 18-0398 Thermostat Gasket

Fitment

• 1987 and newer GM engines with standard cooling requiring a 160 degree F thermostat

Replaces (OEM)

• Mallory 9-43157
• Mercury Marine 807252Q5

Frequently Asked Questions

What does the Sierra 18-3647 Thermostat Kit fit? The 18-3647 kit is designed for 1987 and newer GM engines with a standard cooling system that requires a 160 degree F thermostat.

What temperature rating is the thermostat in kit 18-3647? The thermostat included in the 18-3647 kit is rated at 160 degrees F, matching the standard cooling requirement of the applicable GM engines.

What is included in the Sierra 18-3647 Thermostat Kit? The kit contains one 160 degree F thermostat, an 18-7173 O-ring, and four gaskets: 18-2552, 18-2553, 18-2844 thermostat cover gaskets and an 18-2917 thermostat housing gasket, plus an 18-0398 thermostat gasket.

Does this kit replace Mallory or Mercury Marine parts? Yes, the 18-3647 kit corresponds to Mallory number 9-43157 and Mercury Marine number 807252Q5.

Is this thermostat kit suitable for closed cooling systems? No. The 18-3647 kit's thermostat is rated for standard cooling systems requiring a 160 degree F thermostat, not closed cooling applications.

How much does the 18-3647 Thermostat Kit weigh? The Sierra 18-3647 Thermostat Kit weighs 0.32 pounds.

What are the dimensions of the Sierra 18-3647 kit packaging? The kit measures 5 x 5 x 3 inches.

Do I need to replace all the gaskets when installing a new thermostat? Yes, replacing the gaskets and O-ring alongside the thermostat is recommended, which is why the 18-3647 kit bundles the thermostat, O-ring, and matching gaskets together for a complete service.

Is the Sierra 18-3647 an OEM or aftermarket part? The 18-3647 is manufactured by Sierra to meet or exceed the specification of the original equipment thermostat and gaskets it replaces.

What category does the 18-3647 Thermostat Kit belong to? The 18-3647 is listed under Mercruiser Thermostats & Gaskets.