Thermostat 143°F (62°C) – Fits Yamaha 2-Stroke 9.9-55 HP (Replaces 6F5-12411-01, 6F5-12411-02, 6F5-12411-03)

Thermostat 143°F (62°C) – Fits Yamaha 2-Stroke 9.9-55 HP (Replaces 6F5-12411-01, 6F5-12411-02, 6F5-12411-03)

This thermostat is designed for a wide range of Yamaha 2-Stroke outboards from 9.9 to 55 HP, manufactured between 1986 and 1997. This includes specific models such as the 9.9/15 HP (1986–1995), C25/C30 (1990–1997), C40/C55 (1990–1997), and the CV25/CV30/CV40/CV55 series (1989–1990).

It serves as a direct replacement for Yamaha parts 6F5-12411-01-00, 6F5-12411-02-00, and 6F5-12411-03-00, as well as aftermarket equivalents like Sierra Marine 18-3625 and Quicksilver 814554T01.

• Includes one thermostat and one O-ring gasket for a complete installation.
• Engineered for a precise 143°F (62°C) opening temperature.
• Designed for direct OEM replacement, ensuring a straightforward installation process.

Part Number Cross-Reference

Use this table to confirm equivalent part numbers across OEM and aftermarket brands.

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.

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

Yamaha 2-Stroke Outboards

Mercury/Mariner Compatibility (Crossover Application)

Technical Specifications

Package Contents

• 1 x Thermostat (Replaces 6F5-12411-03-00)
• 1 x O-ring Gasket

Installation Guide

1. Ensure the engine is completely cool before starting work.
2. Disconnect the negative battery cable to prevent accidental starting.
3. Locate the thermostat housing on the engine block. Place a drain pan below it to catch any coolant.
4. Carefully remove the bolts securing the housing cover. A light tap may be needed to break the seal.
5. Remove the old thermostat and gasket. Note the orientation of the thermostat for correct placement of the new one.
6. Thoroughly clean the mating surfaces of the housing and its cover, removing all old gasket material.
7. Install the new thermostat and O-ring gasket, ensuring the thermostat is seated correctly.
8. Re-install the housing cover and tighten the bolts evenly to the manufacturer-specified torque. Do not overtighten.
9. Reconnect the battery cable.
10. Start the engine, let it warm up, and carefully check for any leaks around the thermostat housing.

Troubleshooting & FAQ

How do I confirm this thermostat fits my engine?
A: Check the "Compatible Engine Models" and "Part Number Cross-Reference" tables on this page. It is crucial to match your engine's model, year, and original part number to ensure correct fitment.

What are the signs of a faulty thermostat?
A: Common signs of a failing thermostat include the engine overheating at low speeds, the engine taking too long to reach its normal operating temperature, or an erratic temperature gauge reading.

Is this a 60°C or 62°C thermostat?
A: This thermostat is rated to open at 62°C (143°F). While some OEM parts may vary slightly, this temperature is specified for optimal performance in the listed engine models.

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.