Thermostat Kit with Hoses – Fits Johnson/Evinrude V4 Crossflow 65-140 HP (Replaces 18-3673, 340975, 340976)

Thermostat Kit with Hoses – Fits Johnson/Evinrude V4 Crossflow 65-140 HP

This thermostat kit is designed for Johnson/Evinrude 2-Stroke V4 Crossflow outboard engines, ranging from 65 HP to 140 HP (including Jet models), for model years 1978–1995. It provides a reliable solution for maintaining optimal engine operating temperature.

This kit serves as a direct replacement for multiple OEM and aftermarket part numbers, including Johnson/Evinrude 18-3673, Sierra 18-3673, GLM 13270, OMC 434841, and HeuroFosh 18-3673.

• Includes a complete set of components with both starboard and port hoses for a full replacement.
• Engineered for direct, hassle-free installation with factory OEM-style fittings.
• Features thermostats rated for a 143°F (62°C) operating temperature to ensure correct engine performance.

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

• 2 x Thermostat (Replaces 393659, 434841, 378065, 508626, 5005440, 18-3543)
• 2 x Gasket (Replaces 332369, 18-0977)
• 2 x Thermostat Gasket (Replaces 321932, 18-0675)
• 2 x Poppet Relief Valve (Replaces 318395, 18-3564)
• 2 x Grommet (Replaces 321692, 18-2391)
• 2 x Valve Spring (Replaces 317245, 18-1243)
• 1 x Starboard Hose (Replaces 340975, 18-70936, 321724)
• 1 x Port Hose (Replaces 340976, 18-70937)

Installation Guide

1. Safety First: Disconnect the battery cables before beginning any work.
2. Drain Coolant: Partially drain the engine's cooling system to a level below the thermostat housing.
3. Access Housing: Locate and remove the thermostat housing cover(s). This may require removing other components for access.
4. Remove Old Components: Carefully take out the old thermostats, gaskets, and poppet valve assemblies. Note their orientation.
5. Remove Hoses: Disconnect and remove the old starboard and port hoses.
6. Clean Surfaces: Thoroughly clean the gasket mating surfaces on the engine block and housing covers.
7. Install New Components: Install the new thermostats, springs, poppet valves, and gaskets in the correct order and orientation.
8. Attach New Hoses: Connect the new starboard and port hoses to their respective fittings, ensuring they are securely clamped.
9. Reassemble: Reinstall the thermostat housing cover(s) and tighten the bolts to the manufacturer's specified torque.
10. Refill and Reconnect: Refill the cooling system with the appropriate coolant. Reconnect the battery.
11. Test for Leaks: Start the engine and let it reach operating temperature. Carefully check for any coolant leaks from the housing or hoses.

Troubleshooting & FAQ

How can I be sure this thermostat kit fits my Johnson/Evinrude engine?
This kit is specifically made for Johnson/Evinrude V4 Crossflow engines from 65-140 HP, manufactured between 1978 and 1995. The most reliable method is to check your engine's model, horsepower, and year against the "Compatible Engine Models" table. Cross-referencing the part numbers (like 18-3673) with your service manual or the old part is also highly recommended.

What is the operating temperature of this thermostat?
The thermostats in this kit are rated for 143°F (62°C). This temperature is specified for these engines to ensure they warm up correctly and maintain optimal temperature during operation, which is critical for performance and fuel efficiency.

What are the signs my old thermostat is failing?
Common symptoms include the engine overheating at various speeds, the temperature gauge reading higher or lower than normal, or the engine taking an unusually long time to warm up. You might also notice coolant leaking from the thermostat housing area.

OEM vs. Aftermarket?
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.

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

What is your warranty and return policy?
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.