Thermostat – Fits Tohatsu/Mercury/Evinrude 2-6 HP 4-Stroke (Replaces 3H6-01030-0, 804540)

Thermostat – Fits Tohatsu/Mercury/Evinrude 2-6 HP 4-Stroke (Replaces 3H6-01030-0, 804540)

This thermostat is a direct replacement for small 4-stroke outboard engines, including various models from Tohatsu/Nissan, Mercury/Mariner, and Evinrude. It ensures your engine operates at the correct temperature for optimal performance and longevity.

This part is designed to replace Tohatsu 3H6-01030-0 / 345-01030-0, Mercury 804540 / 853704 / 8537041, Evinrude 5040958, and Sierra 18-3638.

• Engine Mount installation
• Standard operating temperature of 52°C (126°F)
• Includes one thermostat

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.

Confirm your engine model/year in the table below.

Confirm your engine model/year in the table below. For Johnson/Evinrude owners, here’s a guide to help you identify your engine’s serial/model: Johnson Serial Number Guide.

Mercury/Mariner

Tohatsu/Nissan

Evinrude

Technical Specifications

Package Contents

• 1 x Thermostat (3H6-01030-0/804540)

Installation Guide

1. Safety First: Ensure the engine is completely cool and disconnected from the battery.
2. Locate Housing: Find the thermostat housing on the engine block, typically near the top where the main coolant hose connects.
3. Drain Coolant: Place a container below and carefully drain a small amount of coolant, just enough so it's below the housing level.
4. Remove Bolts: Loosen and remove the bolts securing the thermostat housing cover.
5. Extract Old Thermostat: Lift the cover and carefully remove the old thermostat and its gasket. Note its orientation.
6. Clean Surfaces: Thoroughly clean the mounting surfaces of the housing and cover, removing any old gasket material or corrosion.
7. Install New Thermostat: Place the new thermostat into the housing, ensuring it is in the correct orientation. Install the new gasket.
8. Secure Cover: Re-position the housing cover and tighten the bolts evenly to the manufacturer's recommended torque. Do not over-tighten.
9. Final Checks: Reconnect any hoses, top off the coolant, and reconnect the battery. Run the engine and check for any leaks around the housing.

Troubleshooting & FAQ

Q: How do I confirm this thermostat fits my engine?
A: Carefully check the detailed compatibility tables for your engine brand, model, horsepower, and year range. It is also critical to cross-reference your existing part number with those listed, such as Tohatsu 3H6-01030-0 or Mercury 804540, to ensure a perfect match.

Q: What are the common signs of a failing thermostat?
A: Symptoms of a faulty thermostat include the engine overheating, especially at higher speeds, or running too cold at idle and low speeds. You might also notice your temperature gauge giving erratic or inconsistent readings.

Q: What is the operating temperature of this unit?
A: This thermostat is rated for a standard operating temperature of 52°C (126°F). This matches the original OEM specifications to ensure your engine maintains its ideal temperature for performance and efficiency.

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.