6FM-12411-00-00 Thermostat for Yamaha F20F F20G F25G | JLM Marine

Thermostat for Yamaha F20F, F20G, F25G Outboard Engines

This aftermarket replacement thermostat is designed to fit Yamaha 4-stroke outboard engines, specifically the 20 HP F20F and F20G models, as well as the 25 HP F25G model. Engineered to maintain optimal engine operating temperature, this thermostat ensures reliable performance and protects your engine from overheating.

Direct OEM Replacement: 6FM-12411-00-00

• Precision-engineered to OEM specifications for reliable temperature regulation
• Essential component for maintaining proper engine cooling
• 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.

Technical Specifications

Package Contents

• 1 × Thermostat (OEM# 6FM-12411-00-00)

Installation Guide

1. Preparation: Ensure the engine is completely cool and disconnect the battery for safety. Gather necessary tools including screwdrivers, wrenches, and a drain pan.
2. Drain Coolant: Locate and open the drain plug to drain the cooling system into a suitable container.
3. Access Thermostat Housing: Remove the engine cover and locate the thermostat housing, typically on the cylinder head. Disconnect any hoses or clamps attached to the housing.
4. Remove Old Thermostat: Unbolt and remove the thermostat housing cover. Carefully extract the old thermostat and clean the mating surfaces thoroughly.
5. Install New Thermostat: Position the new thermostat in the housing with the spring side facing the correct direction (refer to your service manual). Ensure proper seating and alignment.
6. Reassemble Housing: Install a new gasket or O-ring if included, then reattach the thermostat housing cover. Torque bolts to manufacturer specifications in a crisscross pattern.
7. Refill Coolant: Close all drain plugs and refill the cooling system with the recommended coolant mixture. Check for proper fluid level.
8. Bleed Air: Start the engine and allow it to reach operating temperature to purge air from the cooling system. Monitor coolant level and top off as needed.
9. Final Check: Inspect all connections for leaks and verify proper engine temperature operation. Reinstall engine cover and reconnect battery.

Troubleshooting & FAQ

Q: How do I confirm this thermostat fits my Yamaha outboard?
A: Verify your engine model is F20F, F20G, or F25G and cross-reference the OEM part number 6FM-12411-00-00 with your engine's parts diagram. Always compare the product images with your original thermostat before purchasing.

Q: What are the signs that my thermostat needs replacement?
A: Common symptoms include engine overheating, slow warm-up times, inconsistent temperature readings, or coolant leaks around the thermostat housing. If your engine runs too hot or too cold, the thermostat may be stuck closed or open.

Q: How often should I replace the thermostat?
A: Thermostats should be inspected during regular maintenance intervals (every 100 hours or annually). Replace immediately if you notice performance issues, or preventatively every 3–5 years depending on usage and operating conditions.

Q: Can I install this myself or do I need a professional?
A: While experienced DIYers can perform this replacement with basic tools and mechanical knowledge, professional installation is recommended to ensure proper coolant system bleeding, correct torque specifications, and leak-free operation.

Q: What's the difference between OEM and aftermarket thermostats?
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.