YIUIY Thermostat for Yamaha 2-Stroke Outboards 3HP-250HP — 2-Piece Copper Replacement, Direct-Fit

YIUIY thermostats are replacement cooling valves engineered to restore correct engine operating temperature in Yamaha 2-stroke outboards from 3HP up to 250HP (sold as a 2-piece set).

When an outboard thermostat fails it can cause inconsistent temperatures and reduced engine performance. This pair of YIUIY thermostats fits a broad range of Yamaha 2-stroke models and replaces many common factory part numbers, offering a durable copper construction and direct-fit design to simplify installation and get your boat back on the water faster.

What models and part numbers does this thermostat replace?

These thermostats cover most Yamaha 2-stroke outboards across small to large horsepower ranges. They are designed to be compatible with numerous OEM references so you can match the replacement easily.

• Compatible horsepower: 3HP to 250HP, including 6HP, 9.9HP, 25HP, 90HP, 150HP, 200HP, and others.
• Replaces popular part numbers such as 688-12411-10-00, 6E5-12411-30-00, 6H3-12411-11-00, 6E5-12411-02-00, and more.
• Sold as a 2-piece set to service multiple outlets or to keep a spare on board.

How does this thermostat affect engine temperature and performance?

The thermostat controls coolant flow so the engine reaches and stays within its optimal temperature range. Proper thermostat function prevents the engine from running too cool, which can harm efficiency and increase wear over time.

• Opens and closes to regulate coolant circulation through the engine block and water jacket.
• Helps maintain stable operating temperature for better fuel efficiency and combustion.
• Prevents chronic under-temperature conditions that can reduce power and increase component stress.

What materials and build quality can I expect from the YIUIY unit?

YIUIY thermostats are manufactured from copper alloy components that match the form and function of factory parts. The choice of materials and adherence to original design dimensions aim to provide reliable service life and straightforward replacement.

• Copper-based construction for corrosion resistance and reliable thermal response.
• Designed to meet OEM geometry for direct fit and easy installation.
• Durability suited for saltwater and freshwater environments when installed correctly.

How do I confirm fitment and install the replacement thermostat?

Confirm the correct part by comparing your engine’s current thermostat part number with the replacement list. Installation typically involves removing the thermostat housing, swapping the unit, and reassembling with proper seals—no special tools usually required.

• Check existing part numbers before purchase to ensure compatibility.
• Follow Yamaha service guidelines for thermostat removal and installation.
• Inspect gaskets and hoses while the housing is open and replace if worn.

Who is this for: Boaters, marine technicians, and DIY enthusiasts who own Yamaha 2-stroke outboards and need a cost-effective, OEM-form replacement thermostat. Ideal for routine maintenance, preventative parts stocking, or swapping a failed thermostat to restore proper engine temperature control. If you’re unsure about fitment, inspect the part number on your engine or contact YIUIY customer support for help before ordering.