Thermostat Kit – Fits Mercury Marine 4-Stroke 8-30 HP Outboards (Replaces 855676002, 8M0119207, 8M0139434, 855676005)

Thermostat Kit – Fits Mercury Marine 4-Stroke 8-30 HP Outboards

This thermostat kit is designed for Mercury Marine 8-30 HP 4-Stroke outboard engines (209cc 2/3-cylinder Carb/EFI models). It is also compatible with select Tohatsu and Nissan 4-Stroke outboards that utilize the same thermostat specifications.

This kit serves as a direct replacement for Mercury part numbers 855676002, 8M0119207, 8M0139434, and 855676005, as well as Tohatsu parts 3NV010300M, 3R3-01030-0, and 3R3010300M.

• Includes a 140°F (60°C) thermostat, gasket, and seals for a complete service.
• Engineered as a direct, drop-in replacement for the original components.
• Cross-references with Sierra 18-43175 and Mallory 9-43175.

Part Number Cross-Reference

Use this table to confirm equivalent part numbers across OEM and aftermarket brands.

Compatible Engine Models

Confirm your engine model/year in the table below. For Mercury owners, here’s a guide to help you identify your engine’s serial/model: Mercury Serial Number Guide. You can also review exploded diagrams to verify part numbers: Mercury Parts Diagrams & Catalog.

Mercury Marine

Tohatsu/Nissan

This kit fits compatible Tohatsu/Nissan 4-Stroke outboards that use part numbers 3NV010300M, 3R3-01030-0, or 3R3010300M. Please verify the part number against your engine's service manual or existing thermostat.

Technical Specifications

Package Contents

• 1 x Thermostat (Replaces 855676002)
• 1 x Thermostat Cover Gasket (Replaces 27-853702005)
• 2 x Thermostat Seals

Installation Guide

1. Drain Coolant: Allow the engine to cool completely and drain the cooling system into a suitable container.
2. Locate Housing: Identify the thermostat housing on the engine block or cylinder head.
3. Remove Cover: Loosen and remove the bolts securing the thermostat cover.
4. Remove Old Parts: Carefully take out the old thermostat, gasket, and any seals. Note the orientation of the thermostat.
5. Clean Surfaces: Thoroughly clean the mating surfaces of the housing and cover, removing all old gasket material and corrosion.
6. Install New Thermostat: Place the new thermostat into the housing in the correct orientation.
7. Install Gasket & Seals: Fit the new gasket and seals into place.
8. Reassemble: Re-install the cover and tighten the bolts to the manufacturer's specified torque.
9. Refill System: Refill the cooling system with the recommended coolant.
10. Check for Leaks: Start the engine and let it warm up, checking carefully for any leaks around the thermostat housing.

Troubleshooting & FAQ

Q: How can I be sure this thermostat kit fits my engine?

A: Start by checking the part numbers listed in our cross-reference table against your service manual or the number stamped on your old part. Also, review the compatible engine models table. For Mercury owners, we provide a link to a serial number guide to help you verify your model and year.

Q: What are the common signs of a bad or failing thermostat?

A: The most common symptoms include the engine overheating or, conversely, taking a very long time to reach its normal operating temperature. You might see warnings on your console or notice inconsistent temperature gauge readings.

Q: What is the temperature rating of this thermostat?

A: This thermostat is rated to open at 60°C (140°F) to regulate engine temperature. Note: Some cross-referenced aftermarket parts like the Sierra 18-43175 may be listed with a 130°F rating, but our kit is specified for the 140°F OEM standard.

Q: OEM vs. Aftermarket?

A: This listing is an aftermarket replacement part (not an OEM component). We build to OEM specifications using comparable-grade materials. Production is done in an ISO9002-certified facility, and each batch is inspected for consistent performance.

Q: How fast do you ship and how much does it cost?

A: We offer fast global shipping—typically 5–15 days worldwide—and standard shipping is free. Expedited options are available at checkout depending on your location.

Q: What is your warranty and return policy?

A: This product includes a 1-year warranty against manufacturing defects under normal use. If something goes wrong, contact our support team with your order details. Returns are accepted within our standard return window (unused & in original condition); please see our policy page or reach out for instructions.

Important Notes

• Verify that the product images and specifications match your original part. If discrepancies exist—even if your model is listed—do not proceed with the purchase.
• This product is an aftermarket replacement part and is not an OEM component.
• Professional installation is recommended to ensure safety and optimal performance.

Why Choose JLM MARINE?

• Quality Assured: As a trusted manufacturer for over 20 years, we supply top marine brands globally.
• Fast Global Shipping: Free delivery worldwide in 5–15 days.
• Direct from Manufacturer: Competitive pricing without compromising quality.