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

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

This thermostat kit is designed for Johnson/Evinrude 65-140 HP V4 Crossflow 2-stroke outboards from 1978–1995. It is also compatible with various 65, 80, and 90 Jet engines and select commercial models, providing a comprehensive solution for engine cooling system maintenance.

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 340975, 340976, 393659, 434841, 378065, 508626, and 5005440.

• Includes a complete set of components for the V4 Crossflow dual thermostat system, including starboard and port hoses.
• Engineered as a direct OEM replacement for straightforward, factory-fit installation.
• Features thermostats rated for a 143°F (62°C) operating temperature to ensure optimal engine performance.

Part Number Cross-Reference

Use this table to confirm equivalent part numbers for the complete kit 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 Thermostat Gasket (Replaces: 321932, 18-0675)
• 2 x Gasket (Replaces: 332369, 18-0977)
• 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. Disconnect the battery and allow the engine to cool completely.
2. Drain the cooling system to prevent spills.
3. Locate and remove the thermostat housing covers typically found on the port and starboard cylinder heads.
4. Carefully remove the old thermostats, gaskets, poppet relief valves, springs, and grommets.
5. Thoroughly clean the mating surfaces of the thermostat housing and covers to ensure a proper seal.
6. Install the new poppet relief valves, springs, and grommets into the housing.
7. Place the new thermostats and gaskets into the cylinder heads. Ensure the thermostats are oriented correctly.
8. Reinstall the thermostat housing covers and tighten the retaining bolts to the manufacturer’s recommended torque specifications.
9. Disconnect the old starboard and port cooling hoses. Note their routing before removal.
10. Install the new hoses and securely fasten the clamps at all connection points.
11. Reconnect the battery terminals.
12. Start the engine in a well-ventilated area (or with a water supply), check for any leaks, and monitor the temperature gauge to ensure the engine warms up to its normal operating temperature of 143°F (62°C).

Troubleshooting & FAQ

Q: How do I confirm this kit fits my V4 Crossflow engine?
A: This kit is designed for Johnson/Evinrude V4 Crossflow outboards (65-140 HP) from 1978–1995. Please check the "Compatible Engine Models" table and cross-reference your engine's model, HP, and year. You should also verify your existing part numbers against those listed in our "Part Number Cross-Reference" section.

Q: What are the signs that my thermostat kit needs replacement?
A: Common signs of a failing thermostat kit include engine overheating, the engine running too cold (not reaching its proper operating temperature), erratic temperature gauge readings, or visible coolant leaks from the thermostat housing or connected hoses.

Q: What is the operating temperature of the thermostats in this kit?
A: The thermostats are rated for an operating temperature of 143°F (62°C). This ensures your engine warms up efficiently and maintains the correct temperature for optimal performance, fuel economy, and longevity.

Q: Are these OEM parts?
A: This is an aftermarket kit built to meet or exceed OEM specifications. It includes all necessary components for a complete replacement of the dual thermostat system in V4 Crossflow engines, offering a reliable alternative to OEM parts.

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.