Thermostat & Gasket Kit – Fits Mercury Marine 8-35 HP (Replaces 855676002, 8M0119207)

$19.99 $31.00

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Thermostat & Gasket Kit – Fits Mercury Marine 8-35 HP (Replaces 855676002, 8M0119207) is backordered and will ship as soon as it is back in stock.

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Product Details

This Thermostat & Gasket Kit – Fits Mercury Marine 8-35 HP Outboard Motors is designed for a precise fit on Mercury Marine 8-35 HP 4-Stroke outboard engines from 2005 to the present, focusing on 209cc 2-cylinder and 3-cylinder models. It is also compatible with select Tohatsu and Nissan 4-Stroke outboards that utilize a 60°C (140°F) thermostat, ensuring your engine maintains its optimal operating temperature for performance and longevity.

This kit serves as a direct interchange for multiple OEM and aftermarket part numbers, including Mercury 855676002, 8M0119207, 8M0139434, Sierra 18-43175, and Tohatsu 3NV010300M, providing a reliable replacement solution.

Engineered as a direct replacement for a straightforward installation process.
Maintains the correct engine operating temperature of 60°C (140°F).
Includes thermostat, gasket, and rubber ring seal 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
Sierra	18-43175
Mallory	9-43175
Tohatsu	3NV010300M
Tohatsu	3R3-01030-0
Tohatsu	3R3010300M

Engine & Model Compatibility

Confirm your engine model/year in the table below.

For Mercury Marine, this kit fits a wide range of 4-stroke models from 8 HP to 35 HP manufactured from 2005 to present. Please verify your engine serial number as noted.

For Tohatsu, this part is compatible with various 4-stroke models from 8 HP to 30 HP that use the specified OEM part numbers.

Brand	Model	Rated HP	Stroke	Years	OEM Part No.	Notes
Mercury	4-Stroke	8	4-Stroke	2005–present	855676002/8M0119207	Serial R042475 & Up
Mercury	4-Stroke	9.9	4-Stroke	2005–present	855676002/8M0119207	Serial R042475 & Up
Mercury	Carb (2cyl)	15	4-Stroke	2005–present	855676002/8M0119207	Serial R235949 & Up
Mercury	SeaPro	15	4-Stroke	2005–present	855676002/8M0119207	Serial R051685 & Up
Mercury	Carb (2cyl)	20	4-Stroke	2005–present	855676002/8M0119207	Serial R235168 & Up
Mercury	EFI (3cyl)	25	4-Stroke	2005–present	855676002/8M0119207	Serial R106999 & Up
Mercury	Jet EFI (3cyl)	25	4-Stroke	2005–present	855676002/8M0119207	Serial R165086 & Up
Mercury	SeaPro	25	4-Stroke	2005–present	855676002/8M0119207	Serial R051710 & Up
Mercury	EFI (3cyl)	30	4-Stroke	2005–2012	855676002/8M0119207	Serial T409000-1B226999
Mercury	SeaPro	30	4-Stroke	2005–present	855676002/8M0119207	209cc models
Mercury	Various	35	4-Stroke	2005–present	855676002/8M0119207	209cc models
Tohatsu	Various	8-30	4-Stroke		3NV010300M/3R3-01030-0	Compatible models

Technical Specs

Product Type: Thermostat Kit with Gaskets
Installation: Direct replacement
Temperature Rating: 60°C (140°F)
Operating Temperature: 60°C (140°F)

What’s in the Box

1 x Thermostat (Replaces 855676002/8M0119207)
1 x Thermostat Cover Gasket (Replaces 27-853702005)
1 x Rubber Ring Seal

Installation Notes

Ensure the engine is off and the battery is disconnected.
Allow the engine to cool completely before beginning work.
Drain the engine coolant into a suitable container.
Locate the thermostat housing on the engine block.
Remove the bolts securing the thermostat cover.
Carefully remove the old thermostat, gasket, and any seals. Note their orientation.
Thoroughly clean the mating surfaces of the thermostat housing and cover.
Install the new thermostat, gasket, and seal in the correct orientation.
Re-secure the thermostat cover and tighten the bolts to the manufacturer's torque specifications.
Refill the cooling system with the recommended coolant.
Reconnect the battery, start the engine, and check for any leaks around the housing.
Monitor the engine temperature to ensure it operates in the normal range.

Troubleshooting & FAQ

How do I confirm this kit fits my specific engine?

The best method is to match your existing part number to one of the direct replacement numbers listed in our Part Number Matrix. Additionally, review the Engine & Model Compatibility table to ensure your model, horsepower, and year range are included. For Mercury models, checking your engine's serial number against the notes provided is crucial for a correct fit.

What are the common signs of a failing thermostat?

Signs of a bad thermostat include engine overheating, the engine not reaching its proper operating temperature (running too cool), erratic temperature gauge readings, and coolant leaks from the thermostat housing area. A thermostat stuck open will prevent the engine from warming up, while one stuck closed will cause overheating.

Is this a 140°F or 60°C thermostat?

Both. The temperature rating is 60° Celsius, which is equivalent to 140° Fahrenheit. This is the standard operating temperature for the specified outboard models to ensure optimal fuel efficiency, performance, and engine health.

How often should a thermostat be replaced?

There is no universal replacement interval. However, it is recommended to inspect the thermostat during routine cooling system maintenance (such as an impeller change) every 2-3 years or 200-300 hours of use. Replace it if you notice corrosion, sticking, or if the engine is experiencing cooling issues.

Is this an OEM part or an aftermarket replacement?

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.

How fast is shipping and what does it cost?

We ship worldwide quickly—typical transit 5–15 days. Standard shipping is free; expedited options appear at checkout where available.

What is the warranty and return policy?

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

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Fast Global Fulfillment — Free standard delivery to most regions in 5–15 days.
Manufacturer-Direct Value — Fair pricing without compromising on materials or QC.

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