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

Product Details

This complete Thermostat Kit – Fits Johnson/Evinrude V4 Crossflow 65–140 HP outboards is a crucial component for maintaining optimal engine temperature. It is specifically designed for 2-stroke V4 Crossflow models manufactured between 1978 and 1995, providing a reliable cooling system overhaul for various engines, including 65, 80, and 90 Jet models and commercial applications.

It serves as a direct interchange for a wide range of part numbers, including Johnson/Evinrude & Sierra 18-3673, GLM 13270, and OMC numbers 340975, 340976, 393659, 434841, 378065, 508626, and 5005440.

• Installs as a direct OEM-style replacement with factory-fit connections.
• Maintains correct engine operating temperature with thermostats rated at 143°F (62°C).
• Includes all necessary components for a dual thermostat system, including starboard and port hoses.

Part Number Matrix

Use this matrix to confirm equivalent references across OEM and aftermarket.

Engine & Model Compatibility

Confirm your engine model/year in the table below.

This kit is designed for the following Johnson/Evinrude V4 Crossflow outboard engines:

Technical Specs

Product Type

Marine Outboard Thermostat Kit

Installation

Direct OEM replacement

Fuel Type

Gasoline

Connection

Factory OEM fit for V4 Crossflow design

Housing Material

Stainless steel (thermostat component)

Housing Color

Silver/metallic

Package Dimensions

Approx. 20.4 × 10.3 × 4.2 cm (8.03 × 4.06 × 1.65 in)

Weight

Approx. 0.23 kg (8.1 oz)

Fitting Type

OEM-style fittings

Operating Temperature

143°F (62°C) thermostat rating

Warranty

Manufacturer dependent, typically 1 year

Other Technical Attributes

Complete kit with starboard and port hoses for V4 Crossflow dual thermostat system

What’s in the Box

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

Installation Notes

1. Disconnect the battery and allow the engine to cool completely before starting.
2. Locate the thermostat housings on the engine. On V4 models, there are typically two.
3. Place a drain pan under the engine and carefully drain the cooling system.
4. Remove the bolts securing the thermostat housing cover(s).
5. Take out the old thermostats, gaskets, poppet valves, and springs. Note their orientation.
6. Thoroughly clean the mating surfaces of the housing and cover, removing any old gasket material.
7. Install the new thermostats, gaskets, and associated components from the kit in the correct order.
8. Replace the port and starboard hoses with the new ones provided.
9. Re-secure the housing covers, tightening the bolts to the manufacturer's specified torque.
10. Refill the cooling system with the appropriate coolant, checking for any leaks.
11. Reconnect the battery, start the engine, and let it run to confirm proper operating temperature.

Troubleshooting & FAQ

Safety & Important Info

• Verify images/specifications vs your original part. If anything differs—even if your model appears compatible—do not purchase.
• This is an aftermarket replacement, not an OEM component.
• Professional installation is recommended for safety and performance.

About Sea Sierra

• Pro-Grade Standards — We supply marine parts engineered to OEM-level tolerances and tested for real-world conditions.
• Fast Global Fulfillment — Free standard delivery to most regions in 5–15 days.
• Manufacturer-Direct Value — Fair pricing without compromising on materials or QC.