Thermostat (60°C/140°F) – Honda, Mercury & Yamaha Outboard Replacement
Thermostat (60°C/140°F) – Honda, Mercury & Yamaha Outboard Replacement is backordered and will ship as soon as it is back in stock.
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Delivery and Shipping
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Thermostat (60°C/140°F) – Honda, Mercury & Yamaha Outboard Repl...
Thermostat (60°C/140°F) – Honda, Mercury & Yamaha Outboard Replacement is backordered and will ship as soon as it is back in stock.
Product Details
This 60°C/140°F marine outboard thermostat is an aftermarket replacement thermostat for selected Honda, Mercury, and Yamaha four-stroke outboard applications. It is intended to help regulate engine operating temperature by beginning to open at approximately 60°C (140°F).
The listed cross-reference numbers include Honda 19300-ZW9-003 and 19300-ZY3-023, Yamaha 6G8-12411 and 66M-12411 series, Mercury 825212 and 855676 series, and Sierra 18-3541. Always compare the original thermostat, engine model, year, and serial-number range before ordering.
- Aftermarket replacement for selected marine outboard applications.
- 60°C (140°F) nominal opening temperature.
- Single thermostat assembly; this listing is not a multi-part kit.
- Designed as a replacement for the applicable original thermostat when the cross-reference and engine conditions match.
Part Number Cross-Reference
The following numbers are provided as reference points only. A number match should be confirmed against the complete engine application before installation.
| Brand | Manufacturer or Aftermarket Number | Reference |
|---|---|---|
| Honda | 19300-ZW9-003 | Listed replacement reference |
| Honda | 19300-ZY3-023 | Listed replacement reference |
| Yamaha | 6G8-12411-00-00 | 6G8-12411 series reference |
| Yamaha | 66M-12411-00-00 | 66M-12411 series reference |
| Mercury | 825212 | 825212 series reference |
| Mercury | 855676 | 855676 series reference |
| Sierra | 18-3541 | Aftermarket cross-reference |
Engine Compatibility
This thermostat is associated with selected four-stroke outboard applications from Honda, Mercury, and Yamaha, including applications listed across approximately 8–255 HP. The available reference information does not establish one universal fitment range for every model, year, stroke configuration, shaft length, or serial-number range.
Before purchase: verify the original thermostat number and the complete engine identification. Model name, horsepower, year, stroke, and serial-number conditions must agree with the applicable parts catalog. Do not rely on horsepower alone.
| Brand | Application Information | Stroke | Reference Numbers | Fitment Note |
|---|---|---|---|---|
| Honda | Selected BF-series outboards, including applications listed from 8 HP through 225 HP | 4-Stroke | 19300-ZW9-003; 19300-ZY3-023 | Confirm model year and serial-number range |
| Mercury | Selected four-stroke outboard applications, including listed 15 HP, 75 HP, and 90 HP references | 4-Stroke | 825212; 855676 | Confirm the exact engine model and original part number |
| Yamaha | Selected four-stroke outboard applications, including listed applications from 9.9 HP through 70 HP | 4-Stroke | 6G8-12411 series; 66M-12411 series | Confirm model year and serial-number range |
Technical Specifications
- Product Type
- Marine outboard engine thermostat
- Opening Temperature
- Approximately 60°C (140°F)
- Product Format
- Single thermostat assembly
- Construction
- Aftermarket replacement construction
- Intended Use
- Selected four-stroke outboard cooling systems where the original thermostat specification matches
- Brand Status
- Aftermarket replacement; not an OEM-branded component
What's in the Box
- 1 × Thermostat assembly, 60°C/140°F rating
A gasket, seal, housing, or other installation hardware is not identified as included. Reuse of sealing components is not recommended unless they are confirmed to be in serviceable condition; obtain the correct gasket separately when required by the engine manufacturer.
Installation Notes
- Allow the engine to cool completely before beginning service.
- Follow the engine manufacturer's service instructions and observe all applicable safety procedures.
- Disconnect the battery according to the manufacturer's recommended procedure.
- Locate the thermostat housing and place a suitable drain pan beneath the service area.
- Remove the housing cover carefully and note the original thermostat orientation.
- Remove the old thermostat and clean the mating surfaces without damaging the housing.
- Install the replacement thermostat in the same orientation as the original.
- Install the correct new gasket or seal if required for the engine application.
- Reinstall the housing and tighten fasteners to the manufacturer's specified torque.
- Restore the cooling-water supply, start the engine, and check for leaks and normal temperature regulation.
Troubleshooting & FAQ
What temperature does this thermostat begin to open?
The thermostat is rated to begin opening at approximately 60°C (140°F). Opening temperature is not the same as the engine's complete operating-temperature range.
How can I tell whether my thermostat may be faulty?
Possible symptoms include overheating, unusually low operating temperature, fluctuating temperature readings, reduced performance, or restricted cooling-water flow. These symptoms can also result from other cooling-system problems, so diagnose the complete system.
Does the package include a gasket?
The package is identified as one thermostat assembly. A gasket or seal is not identified as included and may need to be purchased separately for the specific engine application.
How should I confirm fitment?
Compare the original thermostat number and physical design, then verify the exact engine brand, model, horsepower, year, stroke, and serial-number range in the applicable parts catalog. If any of these conditions differ, confirm compatibility before ordering.
Can the thermostat be tested before installation?
A thermostat can generally be tested in heated water with an accurate thermometer, following the engine manufacturer's service procedure. It should begin opening near its specified 60°C (140°F) rating. Do not use an open flame or exceed the manufacturer's test instructions.
Is this an OEM component?
No. This listing is for an aftermarket replacement thermostat. The manufacturer-branded and aftermarket reference numbers above are provided for identification and cross-reference purposes.
Safety & Important Information
- Work only on a completely cool engine and follow the applicable service manual.
- Confirm fitment using the complete engine identification, not horsepower alone.
- Inspect the housing, gasket surfaces, cooling passages, and related components during installation.
- Do not operate the engine if leaks, overheating, or abnormal temperature behavior remains after installation.
- This is an aftermarket replacement and is not manufactured or branded by Honda, Mercury, Yamaha, or Sierra.
About Sea Sierra
- Marine Replacement Parts — We provide aftermarket components for maintenance and repair applications.
- Application-Focused Information — Use the supplied cross-reference numbers together with your complete engine identification.
- Practical Replacement Solutions — Verify the original part and installation requirements before ordering.
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