Thermostat 62°/143°F – Fits Johnson/Evinrude 9.9–300HP Two-Stroke Outboards (Replaces 0778199, 0394411)

Thermostat 62°/143°F – Fits Johnson/Evinrude 9.9–300HP Two-Stroke Outboards (Replaces 0778199, 0394411)

This thermostat is designed for a wide range of Johnson/Evinrude 9.9–300HP 2-Stroke outboards manufactured between 1985 and 1995. It is compatible with various engine configurations, from two-cylinder to eight-cylinder models, ensuring reliable temperature regulation for optimal engine performance.

This component is a direct replacement for OMC/Johnson/Evinrude part numbers 394411 / 0394411 and 778199 / 0778199. It also cross-references with Sierra 18-1506 and GLM 13190.

• Engineered to open at 62°C (143°F) to maintain correct operating temperature.
• Manufactured with corrosion-resistant materials for durability in marine environments.
• Includes one thermostat for a complete replacement.

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 Johnson/Evinrude owners, here’s a guide to help you identify your engine’s serial/model: Johnson/Evinrude Serial Number Guide.

Technical Specifications

Package Contents

• 1 x Thermostat (Replaces 0778199/0394411)

Installation Guide

1. Safety First: Ensure the engine is completely cool and disconnected from the power source before beginning.
2. Locate Housing: Find the thermostat housing on the engine block, typically near the top of the cylinder head(s).
3. Drain Coolant: Place a container underneath and drain a sufficient amount of coolant to avoid spills.
4. Remove Housing Cover: Loosen and remove the bolts securing the thermostat housing cover.
5. Remove Old Thermostat: Carefully lift out the old thermostat and any associated gasket or seal. 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 in the correct orientation.
8. Replace Gasket: Install a new gasket or seal on the housing.
9. Secure Cover: Re-attach the housing cover and tighten the bolts to the manufacturer's recommended torque specifications.
10. Refill Coolant: Top off the cooling system with the appropriate coolant.
11. Check for Leaks: Start the engine and let it run for a few minutes while carefully checking the housing for any leaks.
12. Verify Operation: Monitor the engine temperature gauge to ensure it warms up to and maintains the correct operating temperature.

Troubleshooting & FAQ

Q: How do I confirm this thermostat fits my engine?
A: The best way is to compare your original part number to the ones listed in our cross-reference table. Also, check your engine's model and year against our compatible models list. Visually comparing your old thermostat to our product images can also help confirm fitment.

Q: What are the signs of a failing thermostat?
A: Common signs include engine overheating, the engine taking too long to warm up to operating temperature, or erratic temperature gauge readings. A thermostat stuck open will prevent the engine from warming up properly, while one stuck closed will cause overheating.

Q: How often should I replace my outboard's thermostat?
A: While there is no fixed interval, it is good practice to inspect the thermostat during regular cooling system service (e.g., every 2-3 years or 200-300 hours). Many technicians recommend replacing it as a preventative measure, especially if you operate in saltwater.

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.