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

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

This aftermarket thermostat is designed for a wide range of Yamaha 2-Stroke outboard motors, covering models from 3 HP to 250 HP manufactured between 1984 and 2009. It is a direct-fit replacement that ensures your engine maintains the proper operating temperature for optimal performance, preventing both overheating and overcooling.

This component directly replaces multiple Yamaha, Sierra, Parsun, and Mallory part numbers, providing broad compatibility for various 2-stroke and 2-stroke HPDI engine models. Please verify your specific model and year in the tables below before ordering.

• Installation Method: Direct replacement for the original thermostat.
• Included Components: The package includes one thermostat, one thermostat housing gasket, and one thermostat seal.
• Operating Temperature: The thermostat begins to open at 50°C (122°F) to regulate engine temperature.

Part Number Cross-Reference

Use this table to confirm equivalent part numbers across OEM and aftermarket brands. This part is a suitable replacement for the following numbers:

Compatible Engine Models

Confirm your engine model/year in the table below. For Yamaha owners, here’s a guide to help you identify your engine’s serial/model: Yamaha Serial Number Guide. You can also review exploded diagrams to verify part numbers: Yamaha Parts Diagrams & Catalog.

Confirm your engine model/year in the table below.

Yamaha 2-Stroke Outboards

Yamaha 2-Stroke HPDI Outboards

Parsun Outboards

Technical Specifications

Package Contents

This kit includes the following components:

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

Installation Guide

Professional installation is recommended. The following are general steps for replacement:

1. Ensure the engine is completely cool before beginning.
2. Locate the thermostat housing, typically on the cylinder head or engine block.
3. Place a catch pan beneath the housing and carefully drain the coolant from the system.
4. Remove the bolts securing the thermostat housing cover. You may need to gently tap the cover to break the seal.
5. Take note of the old thermostat's orientation before removing it from the housing.
6. Remove the old gasket or seal and thoroughly clean both the housing and cover mating surfaces.
7. Install the new thermostat in the correct orientation, followed by the new gasket and seal.
8. Securely reinstall the housing cover and tighten the bolts to the manufacturer's specified torque.
9. Refill the cooling system with the appropriate coolant mixture.
10. Start the engine and let it warm up, carefully checking for any leaks around the thermostat housing.

Troubleshooting & FAQ

How do I confirm this thermostat fits my engine?
The most reliable way is to match your engine's model and year against the compatibility tables on this page. You can also cross-reference your existing part number with our list of direct replacements. If you are unsure, consult the Yamaha Serial Number Guide linked above or contact us with your engine details.

What are the signs of a failing thermostat?
A thermostat can fail in two ways: stuck open or stuck closed. If it's stuck open, your engine may not reach its optimal operating temperature, leading to poor fuel economy and performance. If it's stuck closed, the engine will overheat, which can cause severe damage. Fluctuating temperature gauges are another common symptom.

How often should I replace my outboard's thermostat?
While there is no fixed interval, it is good practice to inspect the thermostat during regular cooling system service. Many mechanics recommend replacing it every 2-3 years or as a preventative measure, especially if you operate in saltwater environments where corrosion is a concern.

What does the 50°C (122°F) temperature rating mean?
This is the designated opening temperature. The thermostat will remain closed until the engine coolant reaches 50°C (122°F), at which point it begins to open and allow coolant to circulate through the radiator to maintain a stable operating temperature.

OEM vs. Aftermarket?
This listing is an aftermarket replacement part (not an OEM component). We build to OEM specifications using comparable-grade materials. Production is done in an ISO9002-certified facility, and each batch is inspected for consistent performance.

How fast do you ship and how much does it cost?
We offer fast global shipping—typically 5–15 days worldwide—and standard shipping is free. Expedited options are available at checkout depending on your location.

What is your warranty and return policy?
This product includes a 1-year warranty against manufacturing defects under normal use. If something goes wrong, contact our support team with your order details. Returns are accepted within our standard return window (unused & in original condition); please see our policy page or reach out for instructions.

Important Notes

• Verify that the product images and specifications match your original part. If discrepancies exist—even if your model is listed—do not proceed with the purchase.
• This product is an aftermarket replacement part and is not an OEM component.
• Professional installation is recommended to ensure safety and optimal performance.

Why Choose JLM MARINE?

• Quality Assured: As a trusted manufacturer for over 20 years, we supply top marine brands globally.
• Fast Global Shipping: Free delivery worldwide in 5–15 days.
• Direct from Manufacturer: Competitive pricing without compromising quality.