Yamaha Outboard Thermostat 60°C (140°F) – 2-Stroke 25D Application – OEM 6F5-12411-03
Yamaha Outboard Thermostat 60°C (140°F) – 2-Stroke 25D Application – OEM 6F5-12411-03 is backordered and will ship as soon as it is back in stock.
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Yamaha Outboard Thermostat 60°C (140°F) – 2-Stroke 25D Application ...
Yamaha Outboard Thermostat 60°C (140°F) – 2-Stroke 25D Application – OEM 6F5-12411-03 is backordered and will ship as soon as it is back in stock.
Product Details
This is an aftermarket Yamaha outboard thermostat rated at 60°C (140°F). It is intended for the cooling system of select Yamaha 2-stroke outboards, including the documented 25D application. The thermostat helps regulate engine operating temperature by controlling coolant flow through the thermostat housing.
The company catalog identifies Yamaha OEM reference 6F5-12411-03 for this thermostat. It is a replacement component, not a genuine Yamaha-branded part.
- Thermostat opening temperature: 60°C (140°F).
- For select Yamaha 2-stroke outboard applications.
- Designed for installation in the engine thermostat housing.
- Verify the exact model and service-manual specification before ordering.
Reference Numbers
Use the following documented references when comparing this replacement with the part being removed.
| Brand or Source | Reference | Type | Notes |
|---|---|---|---|
| Yamaha | 6F5-12411-03 | OEM reference | Primary reference identified in the company product record. |
| Sierra | 18-3625 | Aftermarket reference | Listed in the Sierra catalog with Yamaha reference 6F5-12411-03. |
Engine & Model Compatibility
The confirmed company fitment identifies a Yamaha 2-stroke 25D application. The company application notes also reference Yamaha 20, 25, 30, 40, C40, C50, 225, 250, S225, S250, SX225, SX250, V200, V225, VX200, VX225, VX250, and P40 models. Because the available application note does not provide complete model-year, shaft, or serial-number conditions for every reference, confirm the exact engine model and compare the original thermostat before purchase.
| Brand | Model or Application | Stroke | Temperature | Reference | Fitment Notes |
|---|---|---|---|---|---|
| Yamaha | 25D | 2-Stroke | 60°C (140°F) | 6F5-12411-03 | Confirmed company-record application; verify model details before installation. |
| Yamaha | 20; 25; 30; 40; C40; C50; 225; 250; S225; S250; SX225; SX250; V200; V225; VX200; VX225; VX250; P40 | Not fully specified in the application note | 60°C (140°F) | 6F5-12411-03 | Additional company-listed application references. Confirm the exact year, shaft, serial range, and thermostat specification from the engine identification plate and service information. |
Technical Specifications
- Product Type
- Marine outboard thermostat
- Brand Application
- Yamaha outboard
- Stroke
- 2-stroke for the confirmed 25D application
- Opening Temperature
- 60°C (140°F)
- Primary OEM Reference
- 6F5-12411-03
- Installation Location
- Thermostat housing
- Fuel Type
- Gasoline outboard application
What's in the Box
- 1 x 60°C (140°F) outboard thermostat
Additional gaskets, O-rings, seals, or hardware are not specified in the company package record. Reuse only serviceable components or obtain replacement sealing parts separately according to the engine service manual.
Installation Notes
- Allow the outboard to cool completely and follow the safety procedures in the engine service manual.
- Disconnect the battery if required by the engine manufacturer's service procedure.
- Locate the thermostat housing and place a suitable drain pan beneath the work area to collect water.
- Remove the housing cover carefully and note the orientation of the original thermostat.
- Remove the old thermostat and inspect the housing, sealing surfaces, and related sealing components for corrosion or damage.
- Install the replacement thermostat in the correct orientation. Replace damaged sealing components with the exact parts specified for the engine.
- Reinstall the housing cover and tighten the fasteners to the manufacturer's specified torque.
- Run the engine according to the service-manual procedure and check for leaks, proper water flow, and abnormal temperature warnings.
Troubleshooting & FAQ
What temperature is this thermostat?
This thermostat is rated at 60°C (140°F). The 140°F rating is the correct Fahrenheit conversion of the company-listed 60°C specification; the previous 143°F description has been corrected.
Which engine is confirmed for this part?
The company product record explicitly identifies the Yamaha 2-stroke 25D application. Other Yamaha applications are listed as additional references, but exact year, shaft, serial, and model conditions should be confirmed before ordering.
Is this thermostat for a 4-stroke engine?
No 4-stroke fitment is confirmed for this product record. The documented 25D application is 2-stroke. Do not install this thermostat in a 4-stroke engine unless the manufacturer's parts information specifically confirms compatibility.
Does the package include a gasket or O-ring?
The company package record identifies the product as a single thermostat and does not specify a gasket, O-ring, or seal as included. Check the service manual and obtain the required sealing parts separately if necessary.
How do I know if the thermostat needs replacement?
Possible symptoms include overheating, an abnormal temperature warning, poor temperature regulation, or an engine that does not reach its normal operating temperature. A weak tell-tale stream can have several causes, so inspect the complete cooling system rather than relying on that symptom alone.
Can I install this thermostat myself?
Thermostat replacement may be suitable for a mechanically experienced owner with the correct tools. Always follow the engine service manual, use the specified tightening torque, and seek professional service if the housing or fasteners are corroded or damaged.
Is this a genuine Yamaha part?
No. This is an aftermarket replacement identified for Yamaha applications. Yamaha and Sierra references are provided only for product comparison and compatibility checking.
Shipping speed and cost?
We ship worldwide quickly—typical transit is 5–15 days. Standard shipping is free; expedited options appear at checkout where available.
Warranty and returns?
Covered by a 1-year warranty against manufacturing defects under normal use. If an issue arises, contact support with your order details. Returns are accepted within our standard window when the item is unused and in its original condition. See the applicable policy page or contact support for instructions.
Safety & Important Information
- Confirm the complete engine model, year, shaft, and serial information before ordering whenever available.
- Compare the new thermostat with the original part and verify the specified opening temperature.
- Do not rely on horsepower alone to establish compatibility.
- Do not use this product in a 4-stroke engine unless the manufacturer's parts information confirms it.
- This is an aftermarket replacement, not a genuine Yamaha component.
- Professional installation is recommended when the thermostat housing or sealing surfaces are damaged.
About Sea Sierra
- Pro-Grade Standards — We supply marine replacement parts selected for dependable fit and service in 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 quality control.
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