Thermostat – Fits Yamaha 75-90HP 4-Stroke Outboards (Replaces 6FP-12411-00-00)
Thermostat – Fits Yamaha 75-90HP 4-Stroke Outboards (Replaces 6FP-12411-00-00) is backordered and will ship as soon as it is back in stock.
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Worry-free returns
Worry-free returns
You may return most new, unopened items within 7 days of delivery for a full refund. We'll also pay the return shipping costs if the return is a result of our error (you received an incorrect or defective item, etc.).
You should expect to receive your refund within four weeks of giving your package to the return shipper, however, in many cases you will receive a refund more quickly. This time period includes the transit time for us to receive your return from the shipper (5 to 10 business days), the time it takes us to process your return once we receive it (3 to 5 business days), and the time it takes your bank to process our refund request (5 to 10 business days).
If you need to return an item, simply login to your account, view the order using the "Complete Orders" link under the My Account menu and click the Return Item(s) button. We'll notify you via e-mail of your refund once we've received and processed the returned item.
Delivery and Shipping
Delivery and Shipping
Free standard shipping on all orders under 1 KG
Product Details
This Thermostat – Fits Yamaha 75-90HP 4-Stroke Outboards is a crucial component for maintaining optimal engine temperature. It is specifically designed for Yamaha 4-Stroke outboard models including the 75HP, 90HP, and VF90 series from 2016 through 2023, ensuring reliable performance by regulating coolant flow at a precise 60°C (140°F).
This assembly serves as a direct interchange for several part numbers, including Sierra 18-3641, Mercury 8M0175325, and Mercury 8M6010300.
- Regulates engine operating temperature for peak efficiency.
- Installs within the engine block's cooling system passages.
- Engineered as a direct OEM-equivalent replacement.
Part Number Matrix
Use this matrix to confirm equivalent references across OEM and aftermarket.
| Brand | Part Number | Notes |
|---|---|---|
| Yamaha | 6FP-12411-00-00 | Original OEM Part |
| Sierra | 18-3641 | Aftermarket Cross-Reference |
| Mercury | 8M0175325 | Aftermarket Cross-Reference |
| Mercury | 8M6010300 | Aftermarket Cross-Reference |
Engine & Model Compatibility
Confirm your engine model/year in the table below.
| Brand | Model | Rated HP | Stroke | Years | OEM Part No. | Notes |
|---|---|---|---|---|---|---|
| Yamaha | F75B | 75 | 4-Stroke | 2017–2023 | 6FP-12411-00-00 | |
| Yamaha | F90B | 90 | 4-Stroke | 2016–2023 | 6FP-12411-00-00 | |
| Yamaha | VF90 | 90 | 4-Stroke | 2018–2023 | 6FP-12411-00-00 | VMAX SHO model |
Technical Specs
- Product Type
- Thermostat Assembly
- Installation
- Engine Cooling System
- Temperature Rating
- 60°C (140°F)
- Housing Material
- Metal (Brass)
- Dimensions
- 6.0" x 6.0" x 6.0"
- Operating Temperature
- 60°C (140°F) opening temperature
- Warranty
- Manufacturer's standard warranty
- Other Technical Attributes
- OEM replacement for cooling system water flow regulation
What’s in the Box
- 1 x Thermostat Assembly (6FP-12411-00-00)
Installation Notes
- Ensure the engine is off and completely cool. Disconnect the battery for safety.
- Drain the engine coolant to a level below the thermostat housing.
- Carefully remove the bolts securing the thermostat housing cover.
- Take out the old thermostat, noting its orientation. Remove the old gasket and clean all mating surfaces of residue.
- Install the new thermostat assembly in the correct orientation.
- Re-secure the housing cover with a new gasket, tightening bolts to the manufacturer-specified torque.
- Refill the cooling system with the appropriate coolant.
- Reconnect the battery, start the engine, and check for any leaks while monitoring the temperature gauge.
Troubleshooting & FAQ
How do I know if my thermostat needs replacing?
Signs of a failing thermostat include engine overheating (stuck closed), the engine not reaching operating temperature (stuck open), or erratic readings on your temperature gauge.
Is this the correct temperature rating for my engine?
This thermostat opens at 60°C (140°F), which is the specified temperature for the compatible Yamaha models listed. Using the correct temperature is vital for engine performance and longevity.
Can this part resolve an overheating issue?
If the overheating is caused by a faulty thermostat that is stuck closed, then yes, replacing it should resolve the problem. However, overheating can also be caused by other issues like a bad water pump, blockages, or low coolant.
What happens if I use the wrong thermostat?
Using a thermostat with the wrong temperature rating can lead to poor engine performance, increased fuel consumption, and potential engine damage over time. Always match the part number or specification.
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.
Payment & Security
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