Marine Thermostat – Fits Yamaha F300/F350 4-Stroke V8 (Replaces 6AW-12411-00-00, 18-3634)
Marine Thermostat – Fits Yamaha F300/F350 4-Stroke V8 (Replaces 6AW-12411-00-00, 18-3634) is backordered and will ship as soon as it is back in stock.
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Delivery and Shipping
Delivery and Shipping
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Marine Thermostat – Fits Yamaha F300/F350 4-Stroke V8 (Replaces 6AW...
Marine Thermostat – Fits Yamaha F300/F350 4-Stroke V8 (Replaces 6AW-12411-00-00, 18-3634) is backordered and will ship as soon as it is back in stock.
Product Details
This is a direct-replacement Marine Thermostat for Yamaha F300/F350 4-Stroke V8 Outboards, specifically designed to fit 300HP and 350HP V8 engines manufactured between 2007 and 2018. It maintains the correct engine operating temperature for optimal performance and fuel efficiency.
It serves as a direct replacement for Yamaha part number 6AW-12411-00-00 and Sierra part number 18-3634.
- Engineered for direct OEM replacement fitment.
- Regulates coolant temperature to 60°C / 140°F.
- Designed for use in Yamaha V8 outboard cooling systems.
Part Number Matrix
Use this matrix to confirm equivalent references across OEM and aftermarket.
| Brand | Part Number |
|---|---|
| Yamaha | 6AW-12411-00-00 |
| Sierra | 18-3634 |
Engine & Model Compatibility
Confirm your engine model/year in the table below.
This thermostat is compatible with a range of Yamaha V8 4-stroke outboards from 300HP to 350HP.
| Brand | Model | Rated HP | Stroke | Years | OEM Part No. | Notes |
|---|---|---|---|---|---|---|
| Yamaha | F300TUR | 300 | 4-Stroke | 2007–2009 | 6AW-12411-00-00 | |
| Yamaha | F300TXR | 300 | 4-Stroke | 2007–2009 | 6AW-12411-00-00 | |
| Yamaha | LF300TUR | 300 | 4-Stroke | 2007–2009 | 6AW-12411-00-00 | |
| Yamaha | LF300TXR | 300 | 4-Stroke | 2007–2009 | 6AW-12411-00-00 | |
| Yamaha | F350TUR | 350 | 4-Stroke | 2007–2009 | 6AW-12411-00-00 | |
| Yamaha | F350TXR | 350 | 4-Stroke | 2007–2009 | 6AW-12411-00-00 | |
| Yamaha | LF350TUR | 350 | 4-Stroke | 2007–2009 | 6AW-12411-00-00 | |
| Yamaha | LF350TXR | 350 | 4-Stroke | 2007–2009 | 6AW-12411-00-00 | |
| Yamaha | F350AET1U | 350 | 4-Stroke | 2010 | 6AW-12411-00-00 | |
| Yamaha | F350AET1X | 350 | 4-Stroke | 2010 | 6AW-12411-00-00 | |
| Yamaha | FL350AET1U | 350 | 4-Stroke | 2010 | 6AW-12411-00-00 | |
| Yamaha | FL350AET1X | 350 | 4-Stroke | 2010 | 6AW-12411-00-00 | |
| Yamaha | F350UCA | 350 | 4-Stroke | 2010–2011 | 6AW-12411-00-00 | |
| Yamaha | F350XCA | 350 | 4-Stroke | 2010–2011 | 6AW-12411-00-00 | |
| Yamaha | LF350UCA | 350 | 4-Stroke | 2010–2011 | 6AW-12411-00-00 | |
| Yamaha | LF350XCA | 350 | 4-Stroke | 2010–2011 | 6AW-12411-00-00 | |
| Yamaha | F350UCB | 350 | 4-Stroke | 2012–2015 | 6AW-12411-00-00 | |
| Yamaha | F350XCB | 350 | 4-Stroke | 2012–2015 | 6AW-12411-00-00 | |
| Yamaha | LF350UCB | 350 | 4-Stroke | 2012–2015 | 6AW-12411-00-00 | |
| Yamaha | LF350XCB | 350 | 4-Stroke | 2012–2015 | 6AW-12411-00-00 | |
| Yamaha | F350NCB | 350 | 4-Stroke | 2014–2015 | 6AW-12411-00-00 | |
| Yamaha | F350UCC | 350 | 4-Stroke | 2016–2018 | 6AW-12411-00-00 | |
| Yamaha | F350XCC | 350 | 4-Stroke | 2016–2018 | 6AW-12411-00-00 | |
| Yamaha | F350NCC | 350 | 4-Stroke | 2016 | 6AW-12411-00-00 | |
| Yamaha | LF350UCC | 350 | 4-Stroke | 2016–2018 | 6AW-12411-00-00 | |
| Yamaha | LF350XCC | 350 | 4-Stroke | 2016–2018 | 6AW-12411-00-00 |
Technical Specs
- Product Type
- Marine Thermostat
- Installation
- Direct OEM Replacement
- Fuel Type
- Gasoline
- Operating Temperature
- 60°C / 140°F
- Other Technical Attributes
- For Yamaha V8 outboard cooling systems
What’s in the Box
- 1 × 60°C / 140°F Outboard Thermostat (6AW-12411-00-00)
Installation Notes
- Ensure the engine is completely cool and disconnect the battery.
- Drain the engine coolant into a suitable container.
- Locate the thermostat housing on the engine block.
- Remove the bolts securing the housing cover. Note their positions if they are different lengths.
- Carefully remove the old thermostat and gasket. Take note of its orientation.
- Clean both the housing and cover surfaces thoroughly, removing all old gasket material.
- Install the new thermostat in the correct orientation.
- Place a new gasket on the housing, and then re-install the cover and bolts.
- Refill the cooling system with the manufacturer-recommended coolant.
- Reconnect the battery, start the engine, and check for any leaks as it warms up.
Troubleshooting & FAQ
How do I know if my thermostat is failing?
Common signs of a faulty thermostat include the engine overheating at low speeds, the temperature gauge showing inconsistent readings, or the engine failing to reach its normal operating temperature (running too cold).
Is this the correct temperature rating for my engine?
This thermostat is rated for 60°C / 140°F, which is the specified temperature for the listed Yamaha V8 models. Using the correct temperature thermostat is crucial for engine performance and longevity.
Do I need a new gasket for installation?
Yes, it is highly recommended to use a new thermostat housing gasket during installation to ensure a proper, leak-free seal. Gaskets are typically sold separately.
Why is my engine still overheating after replacing the thermostat?
If overheating persists, check for air trapped in the cooling system, which may need bleeding. Other potential causes include a faulty water pump, clogged cooling passages, or incorrect installation. Ensure the thermostat was installed in the correct orientation.
OEM vs. Aftermarket?
This listing is an aftermarket replacement (not OEM). Built to OEM-level specifications with comparable materials. Manufactured in an ISO 9002 facility, batch-inspected for consistency.
Shipping speed & cost?
We ship worldwide quickly—typical transit 5–15 days. Standard shipping is free; expedited options appear at checkout where available.
Warranty & returns?
Covered by a 1-year warranty against manufacturing defects under normal use. If issues arise, contact support with your order details. Returns are accepted within our standard window (unused & in original condition). See our policy page or reach out for instructions.
Safety & Important Info
- Verify images/specifications vs your original part. If anything differs—even if your model appears compatible—do not purchase.
- This is an aftermarket replacement, not an OEM component.
- Professional installation is recommended for safety and performance.
About Sea Sierra
- Pro-Grade Standards — We supply marine parts engineered to OEM-level tolerances and tested for real-world conditions.
- Fast Global Fulfillment — Free standard delivery to most regions in 5–15 days.
- Manufacturer-Direct Value — Fair pricing without compromising on materials or QC.
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