60°C/140°F Thermostat for Mercury/Mariner 75, 80, 90, 100 & 225 HP 4-Stroke Outboards — Replaces 8M6010296, 855676004, 8M0175321 & 8556761
60°C/140°F Thermostat for Mercury/Mariner 75, 80, 90, 100 & 225 HP 4-Stroke Outboards — Replaces 8M6010296, 855676004, 8M0175321 & 8556761 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.
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60°C/140°F Thermostat for Mercury/Mariner 75, 80, 90, 100 & 225...
60°C/140°F Thermostat for Mercury/Mariner 75, 80, 90, 100 & 225 HP 4-Stroke Outboards — Replaces 8M6010296, 855676004, 8M0175321 & 8556761 is backordered and will ship as soon as it is back in stock.
Product Details
This 60°C (140°F) marine engine thermostat is designed for selected Mercury and Mariner 4-stroke outboard applications in 75, 80, 90, 100 and 225 HP ratings. It is a single replacement thermostat, not a multi-piece kit.
The thermostat begins opening at approximately 60°C (140°F) and helps the cooling system maintain the engine's intended operating temperature. Always compare the complete engine model and serial-number range before ordering.
- 60°C (140°F) opening temperature.
- Replacement thermostat for selected Mercury and Mariner outboard applications.
- Customer-facing references include Mercury numbers 8M6010296, 855676004, 8M0175321 and 8556761.
- Sold as the thermostat only; gasket or seal is not included unless separately specified for the application.
Part Number Matrix
These are the manufacturer and aftermarket references listed for this product. Reference numbers alone do not replace model and serial-number verification.
| Brand | Part Number | Reference Type |
|---|---|---|
| Mercury | 8M6010296 | Manufacturer reference |
| Mercury | 855676004 | Manufacturer reference |
| Mercury | 8M0175321 | Manufacturer reference |
| Mercury | 8556761 | Manufacturer reference |
| Sierra | 18-3632 | Listed aftermarket reference; verify against the engine serial number |
Engine & Model Compatibility
The company product record lists Mercury Mariner fitment for 75, 80, 90, 100 and 225 HP engines. The catalog applications below provide specific Mercury 4-stroke model and serial-number conditions for the listed reference numbers. Do not treat a horsepower match without the serial range as confirmed fitment.
| Brand | Model | Rated HP | Stroke | Reference | Serial Number Condition |
|---|---|---|---|---|---|
| Mercury | 75 EFI | 75 | 4-Stroke | 855676004 | 1B172291 through 1B366822 |
| Mercury | 80 EFI | 80 | 4-Stroke | 855676004 | 1B227000 through 1B366822 |
| Mercury | 90 EFI | 90 | 4-Stroke | 855676004 | 1B172291 through 1B366822 |
| Mercury | 100 EFI | 100 | 4-Stroke | 855676004 | 1B227000 through 1B366822 |
| Mercury | 75 | 75 | 4-Stroke | 8556761 | 0G960500 through 0T800999 |
| Mercury | 75 | 75 | 4-Stroke | 8556761 | 0T801000 through 1B226999 |
| Mercury | 90 | 90 | 4-Stroke | 8556761 | 0G960500 through 0T800999 |
| Mercury | 90 | 90 | 4-Stroke | 8556761 | 0T801000 through 1B226999 |
| Mercury | 225 EFI | 225 | 4-Stroke | 8556761 | 0T653945 and up |
Mariner applications are included in the company fitment record, but a complete Mariner model and serial-number range is not stated there. Confirm the original thermostat reference, engine model and serial number before installation.
Technical Specs
- Product Type
- Marine engine thermostat
- Product Configuration
- Single thermostat; not a multi-piece kit
- Brand Application
- Mercury and Mariner
- Horsepower Applications
- 75, 80, 90, 100 and 225 HP
- Stroke
- 4-Stroke applications listed in the supporting engine catalogs
- Opening Temperature
- 60°C (140°F)
- Installation
- Replacement thermostat; application-specific installation
What's in the Box
- 1 x 60°C (140°F) thermostat
Gaskets, seals, housing components and other hardware are not included unless specifically stated for the selected application.
Installation Notes
- Allow the engine to cool completely before beginning service.
- Confirm the engine model, stroke, serial number and original thermostat reference.
- Follow the manufacturer's service procedure to access the thermostat housing or cylinder-head area.
- Note the orientation of the original thermostat before removal.
- Remove the old thermostat and clean the mating surfaces without damaging the housing.
- Install the replacement thermostat in the correct orientation.
- Use the correct application-specific gasket or seal; it is not included with this thermostat.
- Reassemble and tighten fasteners to the engine manufacturer's specifications.
- Run the engine according to the service procedure, check for leaks and confirm normal temperature operation.
Troubleshooting & FAQ
What does a thermostat do?
A thermostat controls coolant flow so the engine can warm up and remain within its intended operating-temperature range.
What does the 60°C (140°F) rating mean?
It is the approximate temperature at which this thermostat begins to open. Use the temperature specified for your exact engine application.
How can I tell whether this thermostat fits my engine?
Match the complete engine brand, model, horsepower, 4-stroke configuration, serial number and original part reference. Horsepower alone is not sufficient to confirm fitment.
Is this a thermostat kit?
This listing contains one thermostat. It does not include a gasket, seal, housing or other installation hardware unless separately stated.
Can I test the old thermostat?
A qualified technician can test a removed thermostat in temperature-controlled water using the manufacturer's service procedure. Replace it if it does not begin opening at the specified temperature or does not open and close correctly.
When should the thermostat be replaced?
Inspect it whenever the cooling system is serviced or when overheating, low operating temperature, temperature fluctuation or related warning symptoms occur. Follow the engine manufacturer's maintenance recommendations.
Is this an OEM component?
This product is a replacement thermostat. The listed Mercury and Sierra numbers are reference numbers for identification and compatibility; the replacement should not be represented as a genuine OEM-branded component.
Safety & Important Information
- Verify the model, stroke, serial number and original thermostat reference before purchase.
- Do not rely on horsepower alone when confirming compatibility.
- Allow the engine to cool before opening any cooling-system component.
- Use the correct gasket or seal and follow the manufacturer's torque and service instructions.
- Professional installation is recommended when the correct procedure or fitment is uncertain.
About Sea Sierra
- Marine Replacement Parts — We provide replacement components for common marine engine service applications.
- Application-Focused Information — Compare model, stroke and serial-number details before ordering.
- Practical Support — Use the listed manufacturer and aftermarket references to help identify the correct replacement.
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