6F5-12411-03 Thermostat Kit for Yamaha 25D | JLM Marine

Thermostat Kit for Yamaha 25D – 6F5-12411-03

This thermostat kit is designed for Yamaha 2-stroke 25D outboard engines, providing reliable temperature regulation to protect your motor from overheating. It includes all essential components for a complete thermostat service, ensuring proper cooling system performance and engine longevity.

This kit directly replaces multiple Yamaha OEM part numbers, including 6F5-12411-01, 6F5-12411-02, and 6F5-12411-03, along with compatible housing gaskets. It offers a cost-effective aftermarket solution for maintaining your outboard's cooling system.

• Complete service kit with thermostat, seal, and housing gasket
• Direct replacement for Yamaha OEM part numbers
• Designed for Yamaha 2-stroke 25D outboards

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

This complete thermostat service kit includes:

• 1 × Outboard Thermostat
• 1 × Thermostat Seal
• 1 × Thermostat Housing Gasket (Gasket color may be black or blue, but the material is the same)

Installation Guide

1. Disconnect the battery and allow the engine to cool completely before beginning work.
2. Locate the thermostat housing on your Yamaha 25D outboard, typically on the cylinder head or mid-section.
3. Remove the bolts securing the thermostat housing cover using the appropriate socket or wrench.
4. Carefully lift off the housing cover and remove the old thermostat and gasket. Inspect the housing for corrosion or damage.
5. Clean all mating surfaces thoroughly, removing old gasket material and debris to ensure a proper seal.
6. Install the new thermostat seal onto the thermostat, ensuring it seats correctly in the groove.
7. Position the new thermostat into the housing with the temperature-sensing element (spring side) facing the correct direction as indicated by the old unit.
8. Place the new thermostat housing gasket onto the housing, aligning all bolt holes properly.
9. Reinstall the thermostat housing cover, ensuring proper alignment with the gasket.
10. Tighten the housing bolts in a crisscross pattern to the manufacturer's recommended torque specification to prevent warping.
11. Reconnect the battery and start the engine, allowing it to reach operating temperature while monitoring for leaks.
12. Check coolant levels and top off if necessary, then verify proper engine temperature operation.

Troubleshooting & FAQ

Q: How do I confirm this thermostat kit fits my Yamaha outboard?
A: Verify that your engine is a Yamaha 2-stroke 25D model. Cross-reference your current thermostat part number with the listed OEM numbers (6F5-12411-01, 6F5-12411-02, 6F5-12411-03) to ensure compatibility.

Q: How often should I replace my outboard thermostat?
A: Thermostats should be inspected annually and replaced every 2-3 years or when you notice overheating issues, inconsistent temperature readings, or visible corrosion. Regular replacement prevents costly engine damage from cooling system failure.

Q: What are the signs that my thermostat is failing?
A: Common symptoms include engine overheating, running too cool (prolonged warm-up), steam from the engine, reduced performance, or the overheat alarm activating. If you experience any of these, inspect and replace the thermostat immediately.

Q: Why does the gasket color vary between black and blue?
A: The gasket color may vary by production batch, but both black and blue gaskets are manufactured from the same material specification and provide identical sealing performance. Use whichever color is supplied in your kit with confidence.

Q: Is this an OEM part or aftermarket replacement?
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.