Thermostat Repair Service Kit – Fits Mercury Marine 4-Stroke 8-30 HP (Replaces 855676002, 8M0119207, 8M0139434, 855676005)
Thermostat Repair Service Kit – Fits Mercury Marine 4-Stroke 8-30 HP (Replaces 855676002, 8M0119207, 8M0139434, 855676005) is backordered and will ship as soon as it is back in stock.
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Worry-free returns
Worry-free returns
You may return most new, unopened items within 7 days of delivery for a full refund. We'll also pay the return shipping costs if the return is a result of our error (you received an incorrect or defective item, etc.).
You should expect to receive your refund within four weeks of giving your package to the return shipper, however, in many cases you will receive a refund more quickly. This time period includes the transit time for us to receive your return from the shipper (5 to 10 business days), the time it takes us to process your return once we receive it (3 to 5 business days), and the time it takes your bank to process our refund request (5 to 10 business days).
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Delivery and Shipping
Delivery and Shipping
Free standard shipping on all orders under 1 KG
Thermostat Repair Service Kit – Fits Mercury Marine 4-Stroke 8-30 H...
Product Details
This is a complete Thermostat Repair Service Kit – Fits Mercury Marine 4-Stroke 8-30 HP Carb/EFI Outboards. It is designed for Mercury Marine 4-stroke outboards including 8, 9.9, 15, 20, 25, and 30 HP models with 209cc 2/3 cylinder Carbureted and EFI engines. It is also compatible with Tohatsu 4-stroke outboards that use a thermostat with the same temperature rating.
This kit serves as a direct replacement for Mercury part numbers 855676002, 8M0119207, 8M0139434, 855676005; Tohatsu 3NV010300M, 3R3-01030-0, 3R3010300M; Sierra 18-43175; and Mallory 9-43175.
- Engineered for direct-fit installation.
- Maintains factory specified engine temperature of 60°C (140°F).
- Includes thermostat, cover gasket, and seals for a complete service.
Part Number Matrix
Use this matrix to confirm equivalent references across OEM and aftermarket.
| Brand | Part Number |
|---|---|
| Mercury | 855676002 |
| Mercury | 8M0119207 |
| Mercury | 8M0139434 |
| Mercury | 855676005 |
| Tohatsu | 3NV010300M |
| Tohatsu | 3R3-01030-0 |
| Tohatsu | 3R3010300M |
| Sierra | 18-43175 |
| Mallory | 9-43175 |
Engine & Model Compatibility
Confirm your engine model/year in the table below.
This kit is designed to fit a range of Mercury Marine four-stroke carbureted and EFI outboards.
| Brand | Model | Rated HP | Stroke | Years | OEM Part No. | Notes |
|---|---|---|---|---|---|---|
| Mercury | 4-Stroke | 8 | 4-Stroke | 855676002/8M0119207/8M0139434 | 209cc 2-cyl engines | |
| Mercury | 4-Stroke | 9.9 | 4-Stroke | 855676002/8M0119207/8M0139434 | 209cc 2-cyl engines | |
| Mercury | 4-Stroke | 15 | 4-Stroke | 855676002/8M0119207/8M0139434 | 209cc 2/3-cyl engines | |
| Mercury | 4-Stroke | 20 | 4-Stroke | 855676002/8M0119207/8M0139434 | 209cc 2/3-cyl engines | |
| Mercury | 4-Stroke | 25 | 4-Stroke | 855676002/8M0119207/8M0139434 | 209cc 2/3-cyl engines | |
| Mercury | 4-Stroke | 30 | 4-Stroke | 855676002/8M0119207/8M0139434 | 209cc 2/3-cyl engines | |
| Tohatsu | 4-Stroke | 4-Stroke | 3NV010300M, 3R3-01030-0, 3R3010300M | Compatible models |
Technical Specs
- Product Type
- Thermostat Repair Kit
- Installation
- Direct replacement
- Temperature Rating
- 60°C (140°F)
- Operating Temperature
- 60°C (140°F)
What’s in the Box
- 1 x Thermostat (Replaces 855676002)
- 1 x Thermostat Cover Gasket (Replaces 27-853702005)
- 1 x Thermostat Seals (Set)
Installation Notes
- Disconnect the battery before beginning work.
- Allow the engine to cool completely and drain the cooling system.
- Locate the thermostat housing on the engine block.
- Remove the bolts securing the housing cover and carefully lift it off.
- Remove the old thermostat, gasket, and any seals.
- Thoroughly clean the mating surfaces of the housing and cover.
- Install the new thermostat, ensuring it is oriented correctly.
- Place the new gasket and seals into position.
- Re-install the housing cover and tighten bolts to the manufacturer's torque specifications.
- Refill the cooling system, reconnect the battery, and run the engine to check for leaks and proper temperature.
Troubleshooting & FAQ
How can I confirm this kit fits my specific engine?
Verify your engine's horsepower, model, and year against the compatibility chart. The most reliable method is to match the OEM part number from your service manual with the numbers listed in our Part Number Matrix.
What are common symptoms of a bad thermostat?
A thermostat stuck open will prevent the engine from reaching its proper operating temperature, leading to poor performance and fuel economy. A thermostat stuck closed will cause the engine to overheat, which can lead to severe damage.
Some sources say part 8M0139434 only fits 9.9-20hp models. Why do you list it for 8-30hp?
Aftermarket parts are often engineered to cover a broader range of models than a single OEM part number. While Quicksilver may specify a narrower range for 8M0139434, our kit is confirmed to fit the wider 8-30 HP range sharing the same engine block and cooling design. Always verify by your original part number if possible.
What is the operating temperature of this thermostat?
This thermostat is rated to open at 60°C (140°F), which is the standard specification for the listed engine models to ensure optimal performance and longevity.
Are gaskets included with this kit?
Yes, this is a complete repair kit that includes one thermostat, one thermostat cover gasket, and a set of thermostat seals, providing all the necessary components for replacement.
How often should an outboard thermostat be replaced?
There is no fixed replacement interval, but it is good practice to inspect the thermostat during routine cooling system service (e.g., water pump replacement) every 2-3 years, or immediately if you notice temperature-related issues.
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 & 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.
Payment & Security
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