Thermostat Kit for Mercury Marine and Tohatsu 4-Stroke Outboards, 8–30 HP – Replaces 855676002, 8M0119207, 8M0139434 and 855676005
Thermostat Kit for Mercury Marine and Tohatsu 4-Stroke Outboards, 8–30 HP – Replaces 855676002, 8M0119207, 8M0139434 and 855676005 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 Kit for Mercury Marine and Tohatsu 4-Stroke Outboards, 8...
Thermostat Kit for Mercury Marine and Tohatsu 4-Stroke Outboards, 8–30 HP – Replaces 855676002, 8M0119207, 8M0139434 and 855676005 is backordered and will ship as soon as it is back in stock.
Product Details
This aftermarket thermostat kit is intended for selected Mercury Marine, Mercury Mariner and Tohatsu/Nissan 4-stroke outboard applications from 8 to 30 HP. It is associated with Mercury 8 HP and 9.9 HP 209cc 4-stroke engines, Mercury 15 and 20 HP carbureted 2-cylinder 4-stroke engines, and selected 25 and 30 HP EFI, Jet EFI and SeaPro 4-stroke engines. Tohatsu applications include selected MFS8 through MFS30 4-stroke models.
Use the engine model, serial-number range and original manufacturer part number together when confirming fitment. Horsepower alone is not sufficient because the applicable thermostat can vary by engine family and serial range.
- Thermostat service kit for selected Mercury Marine and Tohatsu/Nissan 4-stroke outboards.
- Company-listed temperature specification: 140°F (60°C).
- Aftermarket replacement for the manufacturer and aftermarket references listed below.
- Kit configuration: verify the supplied components against the product images and the parts removed from your engine before installation.
Part Number Matrix
These references are provided to help identify the correct thermostat application. They are not a substitute for checking the complete engine model and serial-number range.
| Brand | Manufacturer or aftermarket reference |
|---|---|
| Mercury Marine | 855676002 |
| Mercury Marine | 8M0119207 |
| Mercury Marine | 8M0139434 |
| Mercury Marine | 855676005 |
| Tohatsu / Nissan | 3R3-01030-0 |
| Tohatsu / Nissan | 3R3010300 |
| Tohatsu / Nissan | 3R3010300M |
| Tohatsu / Nissan | 3NV-01030-0, 3NV010300, 3NV010300M |
| Tohatsu / Nissan | 3SA010300M |
| Sierra | 18-43175 |
Engine & Model Compatibility
The following applications are listed for the thermostat reference family. Keep each model, stroke type and serial condition together when checking your engine.
| Brand | Model/application | Rated HP | Stroke | Serial or year condition | Reference |
|---|---|---|---|---|---|
| Mercury | 8 4-Stroke, 209cc | 8 | 4-Stroke | R042475 & up | 855676002, 8M0119207 |
| Mercury | 9.9 4-Stroke, 209cc | 9.9 | 4-Stroke | R042475 & up | 855676002, 8M0119207 |
| Mercury | 15 Carb, 2-cylinder | 15 | 4-Stroke | R235949 & up | 855676002, 8M0119207 |
| Mercury | 15 SeaPro | 15 | 4-Stroke | R051685 & up | 855676002, 8M0119207 |
| Mercury | 20 Carb, 2-cylinder | 20 | 4-Stroke | R235168 & up | 855676002, 8M0119207 |
| Mercury | 25 EFI, 3-cylinder | 25 | 4-Stroke | R106999 & up | 855676002, 8M0119207 |
| Mercury | 25 Jet EFI, 3-cylinder | 25 | 4-Stroke | R165086 & up | 855676002, 8M0119207 |
| Mercury | 25 SeaPro | 25 | 4-Stroke | R051710 & up | 855676002, 8M0119207 |
| Mercury | 30 EFI, 3-cylinder | 30 | 4-Stroke | T409000–1B226999 | 855676002, 8M0119207 |
| Tohatsu / Nissan | MFS8 through MFS30 applications | 8–30 | 4-Stroke | Confirm the exact model and year | 3R3-01030-0, 3NV010300M |
Technical Specifications
- Product Type
- Thermostat kit
- Application
- Selected Mercury Marine, Mercury Mariner and Tohatsu/Nissan 4-stroke outboards
- Rated Horsepower Range
- 8–30 HP, subject to the model and serial conditions listed above
- Temperature Specification
- 140°F (60°C), according to the company product record
- Installation
- Replacement installation in the thermostat housing; follow the engine service manual
- Product Status
- Aftermarket replacement, not an OEM-branded component
What’s in the Box
This listing is supplied as a thermostat kit. The company records confirm the kit product type but do not provide a definitive component-by-component package list. Check the product images and compare the supplied parts with the parts removed from your engine before beginning service.
Installation Notes
- Confirm the engine model, stroke type, serial number and original part reference before ordering.
- Disconnect the battery where required by the engine service procedure.
- Allow the engine to cool completely before opening the thermostat housing.
- Locate the thermostat housing and remove the cover according to the service manual.
- Remove the old thermostat and any sealing components that are being replaced.
- Clean the mating surfaces without damaging the housing or cylinder block.
- Install the replacement thermostat in the correct orientation.
- Install the applicable sealing components supplied with the kit, if included for your application.
- Reinstall the housing cover and tighten the fasteners to the manufacturer’s torque specification.
- Run the engine using the approved procedure and check for leaks, proper water flow and correct operating temperature.
Troubleshooting & FAQ
How do I confirm that this thermostat kit fits my engine?
Match the complete engine model, horsepower, stroke type and serial-number range to the compatibility information above. If available, also compare the original thermostat or service-manual part number with the listed references.
Does this fit every Mercury or Tohatsu engine between 8 and 30 HP?
No. The horsepower range is only a guide. Fitment depends on the engine family, carbureted or EFI configuration, model designation and serial-number range. Do not use horsepower alone to confirm compatibility.
What temperature specification is listed for this product?
The company product record lists 140°F (60°C). Thermostat specifications can vary between engine applications, so confirm the requirement for your exact engine before installation.
Is this an OEM part?
No. This is an aftermarket replacement kit intended for the applications and reference numbers listed on this page.
Are the included components identical for every application?
The company records identify this product as a thermostat kit but do not publish a definitive component-by-component package list. Review the product images and verify the supplied parts before installation.
What are common symptoms of a thermostat problem?
Possible symptoms include an engine that runs too cool, an engine that overheats, unstable operating temperature or reduced cooling-system performance. Inspect the thermostat and cooling passages as directed by the service manual.
How often should an outboard thermostat be replaced?
Replacement timing depends on the engine manufacturer’s maintenance schedule, operating conditions and inspection results. Replace it when required by the service manual or when testing shows that it is sticking, damaged or outside specification.
Safety & Important Information
- Work only on a completely cool engine and follow the manufacturer’s service procedures.
- Verify the exact engine model, serial number and original part reference before purchase.
- Do not operate the engine if the thermostat housing leaks or the cooling system does not function correctly.
- Professional installation is recommended when the required torque values, sealing procedure or cooling-system checks are unknown.
- This is an aftermarket replacement, not an OEM-branded component.
About Sea Sierra
- Marine Replacement Parts — We supply aftermarket parts for common marine service and repair applications.
- Application-Focused Listings — Product references and fitment conditions are provided to help you compare your engine before ordering.
- Value-Oriented Service — Replacement solutions for routine outboard maintenance and repair.
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