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

Yamaha Outboard Thermostat 143°F/62°C – Fits Yamaha 2-Stroke 9.9-55 HP

This replacement thermostat is designed for a wide range of Yamaha 2-Stroke outboard engines from 9.9 HP to 55 HP, specifically for models manufactured between 1986 and 1997. It ensures your engine maintains the correct operating temperature for optimal performance and longevity.

It serves as a direct replacement for Yamaha OEM part numbers 6F5-12411-01-00, 6F5-12411-02-00, and 6F5-12411-03-00, as well as Sierra part number 18-3625.

• Engineered to operate at 143°F (62°C).
• Direct fitment into the original thermostat housing for straightforward installation.
• Complete kit includes the thermostat, O-ring, and gasket.

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.

Technical Specifications

Package Contents

• 1 x 62°C / 143°F Outboard Thermostat (6F5-12411-03-00)
• 1 x O-ring
• 1 x Gasket (682-12414-A1)

Installation Guide

1. Safety First: Ensure the engine is off and cool, and disconnect the battery.
2. Locate Housing: Find the thermostat housing, typically located on the cylinder head or engine block.
3. Drain Coolant: Place a drain pan under the housing to catch any spilling coolant.
4. Remove Cover: Carefully unbolt and remove the thermostat housing cover.
5. Extract Old Parts: Remove the old thermostat, O-ring, and gasket. Note the orientation of the thermostat.
6. Clean Surfaces: Thoroughly clean the mating surfaces of the housing and cover, removing any old gasket material or corrosion.
7. Install New Parts: Place the new thermostat, gasket, and O-ring into the housing, ensuring correct alignment.
8. Reassemble: Reattach the housing cover and tighten the bolts to the manufacturer's recommended torque specifications.
9. Final Checks: Reconnect the battery, start the engine, and carefully check for leaks as it warms up.

Troubleshooting & FAQ

Q: How do I confirm this thermostat fits my engine?

A: The surest way is to check the compatibility list on this page. Please review the "Compatible Engine Models" table to verify that your Yamaha engine’s model and year range are listed. This part is a confirmed replacement for OEM numbers 6F5-12411-01, 6F5-12411-02, and 6F5-12411-03.

Q: What are the symptoms of a failing outboard thermostat?

A: Common signs of a bad thermostat include the engine overheating (running too hot) or running too cold (not reaching operating temperature). You might notice an alarm from your controls, steam from the engine, or poor performance at idle. The thermostat can fail by being stuck open or stuck closed.

Q: I've seen other thermostats listed at 140°F. Why is this one 143°F?

A: This thermostat is manufactured to the precise OEM specification of 143°F (62°C). While some aftermarket listings may round down to 140°F, our data from multiple technical sources confirms 143°F is the correct temperature for the listed Yamaha models, ensuring your engine operates in its designed temperature range.

Q: OEM vs. Aftermarket?

A: 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.

Q: How fast do you ship and how much does it cost?

A: 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.

Q: What is your warranty and return policy?

A: 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.