Marine Thermostat – Fits Yamaha F300/F350 4-Stroke V8 Outboards (Replaces 6AW-12411-00-00)

Marine Thermostat – Fits Yamaha F300/F350 4-Stroke V8 Outboards

This marine thermostat is designed for Yamaha 4-Stroke 300HP & 350HP V8 outboards manufactured between 2007 and 2018. It ensures your engine maintains the correct operating temperature for optimal performance and longevity.

It serves as a direct replacement for Yamaha part number 6AW-12411-00-00 and Sierra part number 18-3634.

• Installation Method: Direct OEM-style fit
• Operating Temperature: 60°C / 140°F
• Compatible Fuel Type: Gasoline

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 × 60°C / 140°F Outboard Thermostat (Replaces OEM Part #6AW-12411-00-00)

Installation Guide

1. Safety First: Ensure the engine is completely cool and disconnect the battery before starting.
2. Drain Coolant: Place a container under the engine and carefully drain the cooling system to a level below the thermostat housing.
3. Locate Housing: Identify the thermostat housing on the engine block. It is typically connected to the main coolant hoses.
4. Remove Housing Cover: Loosen and remove the bolts securing the thermostat housing cover. Note the orientation of the cover and gasket.
5. Remove Old Thermostat: Carefully lift out the old thermostat and gasket. Clean any sealant residue or corrosion from the housing surfaces.
6. Install New Thermostat: Place the new thermostat into the housing, ensuring it is oriented correctly (the spring side usually faces the engine). Install the new gasket.
7. Reassemble: Secure the housing cover and tighten the bolts to the manufacturer's recommended torque specification. Do not overtighten.
8. Refill and Check: Reconnect hoses if they were removed. Refill the cooling system with the appropriate coolant.
9. Final Inspection: Reconnect the battery. Start the engine and let it warm up, carefully checking for any leaks around the thermostat housing. Top off coolant if necessary.

Troubleshooting & FAQ

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

A: First, check the 'Compatible Engine Models' table on this page to ensure your specific engine model and year range are listed. Second, cross-reference the OEM part number 6AW-12411-00-00 with the part number specified in your engine’s service manual.

Q: What are the common signs of a failing thermostat?

A: Key symptoms include engine overheating alarms, the temperature gauge reading higher or lower than normal, or the engine taking an unusually long time to reach its standard operating temperature. A thermostat stuck open can cause the engine to run too cool, while one stuck closed will lead to overheating.

Q: How often should I replace my outboard's thermostat?

A: As a preventative maintenance measure, we recommend inspecting your thermostat annually and replacing it every 2-3 years, or according to the service interval in your owner's manual. Replacement is especially important for engines used in saltwater environments, where corrosion can cause parts to fail prematurely.

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.