Thermostat – Fits Yamaha 2-Stroke 3-250 HP (Replaces 6E5-12411-02-00, 688-12411-10-00)

Product Details

This Thermostat – Fits Yamaha 2-Stroke 3-250 HP is engineered for a wide range of Yamaha 2-Stroke outboard motors, covering models from 3 HP to 250 HP manufactured between 1984 and 2009. It plays a critical role in maintaining proper engine operating temperature for optimal performance and fuel efficiency.

It serves as a direct replacement for numerous Yamaha, Sierra, Parsun, and Mallory part numbers, ensuring broad interchangeability.

• Installs directly to the engine block for a straightforward fit.
• Designed for use in closed cooling systems.
• Package includes the thermostat, housing gasket, and seal.

Part Number Matrix

Use this matrix to confirm equivalent references across OEM and aftermarket.

Engine & Model Compatibility

Confirm your engine model/year in the table below.

This part fits a variety of Yamaha standard 2-Stroke and HPDI outboards.

Technical Specs

Product Type

Thermostat

Installation

Direct replacement

Fuel Type

Gasoline

Connection

Direct mount to engine block

Housing Material

Brass/stainless steel

Temperature Rating

50°C (122°F) opening temperature

Other Technical Attributes

For closed cooling system

What’s in the Box

• 1 x Thermostat (688-12411)
• 1 x Thermostat Housing Gasket (688-12414)
• 1 x Thermostat Seal (688-12412)

Installation Notes

1. Ensure the engine is completely cool before beginning work.
2. Disconnect the battery to prevent accidental starting.
3. Locate the thermostat housing on the engine block. Place a drain pan underneath to catch any coolant.
4. Remove the bolts securing the housing cover. Note their length and position if they differ.
5. Carefully remove the old thermostat and gasket. Clean both mating surfaces of any old gasket material or corrosion.
6. Install the new thermostat, ensuring it is oriented correctly. Fit the new gasket and seal into place.
7. Re-install the housing cover and tighten the bolts to the manufacturer's specified torque.
8. Reconnect the battery, refill coolant as needed, and check for leaks after starting the engine.

Troubleshooting & FAQ

Safety & Important Info

• Verify images/specifications vs your original part. If anything differs—even if your model appears compatible—do not purchase.
• This is an aftermarket replacement, not an OEM component.
• Professional installation is recommended for safety and performance.

About Sea Sierra

• Pro-Grade Standards — We supply marine parts engineered to OEM-level tolerances and tested for real-world conditions.
• Fast Global Fulfillment — Free standard delivery to most regions in 5–15 days.
• Manufacturer-Direct Value — Fair pricing without compromising on materials or QC.