Sierra 18-3561 Thermostat 105 Degree - Replaces 384719 - Fits Most 3 and 4 Cyl. Outboards 1985-90

The Sierra 18-3561 is a 105 degree F thermostat built as a direct replacement for outboard engine cooling systems. It regulates coolant flow through the powerhead, opening at its rated temperature to maintain consistent operating temperature and protect the engine from overheating or running too cold. This thermostat fits most 3 and 4 cylinder outboard engines from 1985-90 and is a direct replacement for OEM part number 384719.

Installing the correct thermostat is essential for reliable engine performance. A thermostat that fails to open can cause overheating and engine damage, while one that fails to close can prevent the engine from reaching proper operating temperature, leading to poor fuel combustion and increased wear. The Sierra 18-3561 is manufactured to meet or exceed the specifications of the original equipment part it replaces, giving boat owners a dependable option when replacing a worn, stuck, or failed thermostat during routine maintenance.

Specifications

• Brand: Sierra
• Manufacturer Part Number: 18-3561
• Temperature Rating: 105 degrees F
• Replaces (OEM): 384719
• Fitment: Fits most 3 and 4 cylinder outboard engines, 1985-90
• Weight: 0.02 pounds
• Material: Brass
• Color: White
• UPC: 030999753656

Fitment

• Most 3 and 4 cylinder outboard engines, 1985-90

Replaces (OEM)

• 384719

Frequently Asked Questions

What temperature does the Sierra 18-3561 thermostat open at? The Sierra 18-3561 thermostat is rated to open at 105 degrees F, allowing coolant to begin circulating through the powerhead once that temperature is reached.

What engines does the 18-3561 thermostat fit? This thermostat fits most 3 and 4 cylinder outboard engines built from 1985-90.

Is the 18-3561 a direct replacement for the original equipment thermostat? Yes, the Sierra 18-3561 is a direct replacement for OEM part number 384719 and is designed to meet or exceed the performance of the original part.

What is the 18-3561 thermostat made of? The Sierra 18-3561 thermostat is constructed of brass with a white finish.

How much does the 18-3561 thermostat weigh? The Sierra 18-3561 thermostat weighs 0.02 pounds.

How do I know if my outboard thermostat needs to be replaced? Signs that an outboard thermostat like the Sierra 18-3561 needs replacement include the engine running hot, overheating alarms, or the engine taking unusually long to reach normal operating temperature.

Can I install the Sierra 18-3561 myself? The Sierra 18-3561 thermostat is a standard replacement part designed to install in place of the original 384719 thermostat using the same mounting location in the powerhead cooling system.

Does the 18-3561 come with a gasket or seal? The listing for the Sierra 18-3561 covers the thermostat itself; check your engine's cooling system for the correct matching gasket or housing seal when replacing it.

Why does thermostat temperature rating matter on an outboard engine? A thermostat's temperature rating, such as the 105 degree F rating on the 18-3561, determines when coolant begins flowing to regulate engine temperature; using the wrong rating can cause the engine to run too hot or too cold.

Is the Sierra 18-3561 a genuine OEM part or an aftermarket replacement? The Sierra 18-3561 is manufactured by Sierra as a replacement part for OEM number 384719, engineered to meet or exceed original equipment specifications.