Thermostat – Fits Yamaha 75-90HP 4-Stroke (Replaces 6FP-12411-00-00, 18-3641, 775-240)
Thermostat – Fits Yamaha 75-90HP 4-Stroke (Replaces 6FP-12411-00-00, 18-3641, 775-240) is backordered and will ship as soon as it is back in stock.
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Delivery and Shipping
Delivery and Shipping
Orders are typically processed within 1–2 business days.
U.S. orders usually arrive within 6–15 days, depending on stock location and destination.
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Thermostat – Fits Yamaha 75-90HP 4-Stroke (Replaces 6FP-12411-00-00...
Thermostat – Fits Yamaha 75-90HP 4-Stroke (Replaces 6FP-12411-00-00, 18-3641, 775-240) is backordered and will ship as soon as it is back in stock.
Product Details
This replacement Thermostat – Fits Yamaha 75-90HP 4-Stroke Outboards is designed for select Yamaha F75B, F90B, and VF90A 4-cylinder outboard engines manufactured between 2016 and 2022. It ensures your engine maintains the correct operating temperature for optimal performance and longevity.
This component is a direct replacement for OEM part number 6FP-12411-00-00 and interchanges with Sierra 18-3641 and WSM 775-240.
- Engineered for direct-fit installation.
- Regulates engine temperature at 60°C (140°F).
- Constructed with a durable brass housing.
Part Number Matrix
Use this matrix to confirm equivalent references across OEM and aftermarket.
| Brand | Part Number |
|---|---|
| Yamaha | 6FP-12411-00-00 |
| Sierra | 18-3641 |
| WSM | 775-240 |
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 | 2017–2022 | 6FP-12411-00-00 | 4-cylinder engine |
| Yamaha | F90B | 90 | 4-Stroke | 2016–2022 | 6FP-12411-00-00 | 4-cylinder engine |
| Yamaha | VF90A Jet | 90 | 4-Stroke | 2016–2022 | 6FP-12411-00-00 | 4-cylinder jet drive |
Technical Specs
- Product Type
- Outboard Engine Thermostat
- Installation
- Direct replacement
- Operating Temperature
- 60°C (140°F)
- Housing Material
- Brass
- Fitting Type
- Direct fit
- Country of Manufacture
- Japan (OEM); China (some aftermarket)
- Warranty
- Manufacturer-dependent
What’s in the Box
- 1 x Thermostat (6FP-12411-00-00)
Installation Notes
- Disconnect the battery and ensure the engine is completely cool.
- Locate the thermostat housing on the engine block or cylinder head.
- Place a drain pan underneath and remove the housing cover bolts, allowing any remaining coolant to drain.
- Carefully remove the old thermostat and gasket. Note the orientation of the thermostat.
- Clean the mating surfaces of the housing and cover, removing all old gasket material.
- Install the new thermostat in the correct orientation, followed by the new gasket.
- Reattach the housing cover and tighten the bolts to the manufacturer's specified torque.
- Refill the cooling system with the recommended coolant, check for leaks, and reconnect the battery.
Troubleshooting & FAQ
How do I know if my thermostat is failing?
Common signs of a faulty thermostat include engine overheating, running too cool (not reaching operating temperature), erratic temperature gauge readings, and poor engine performance. Visually inspect for corrosion or a stuck-open/closed valve.
Is this thermostat compatible with my engine if it's not in the list?
No. Only purchase this part if your specific engine model and year are explicitly listed in the compatibility table. Using the wrong thermostat can lead to severe engine damage.
Why is the operating temperature listed as 60°C while some sources say 62°C?
Minor variations in reported temperatures can occur between OEM and aftermarket sources. This thermostat is manufactured to operate at the standard 60°C (140°F) specification required for the listed Yamaha models, ensuring correct engine performance. Always defer to the OEM specification for your engine.
What is the recommended replacement interval?
Outboard thermostats do not have a fixed replacement schedule, but they should be inspected during routine cooling system service (typically every 2-3 years or 200-300 hours). It is wise to replace it as a preventative measure if you are already servicing the water pump or cooling passages.
Can I install this myself?
While installation can be done by a mechanically inclined owner, we recommend professional installation to ensure it is done correctly, torqued to spec, and the cooling system is properly bled. An improper installation can cause overheating and engine damage.
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 T& 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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