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

$99.99

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Thermostat Kit with Hoses – Fits Johnson/Evinrude V4 Crossflow 65-140 HP (Replaces 18-3673, 340975, 340976) is backordered and will ship as soon as it is back in stock.

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Product Details

This Thermostat Kit with Hoses – Fits Johnson/Evinrude V4 Crossflow 65-140 HP (Replaces 18-3673, 340975, 340976) is a comprehensive solution designed for Johnson/Evinrude 2-Stroke V4 Crossflow outboard engines from 65 HP to 140 HP, including Jet models, manufactured between 1978 and 1995.

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

Direct replacement with a factory OEM fit for V4 Crossflow designs.
Complete kit contains thermostats, gaskets, hoses, and other essential hardware for a full service.
Features a thermostat rated for 143°F (62°C) to ensure optimal engine operating temperature.

Part Number Matrix

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

Brand	Part Number
Johnson/Evinrude	18-3673
Sierra	18-3673
GLM	13270
OMC	434841
HeuroFosh	18-3673
Johnson/Evinrude Hoses	340975, 340976

Engine & Model Compatibility

Confirm your engine model/year in the table below.

Brand	Model	Rated HP	Stroke	Years	OEM Part No.
Johnson/Evinrude	V4 Crossflow	65 Jet	2-Stroke	1994–1995	340975, 340976, 18-3673
Johnson/Evinrude	V4 Crossflow	80 Jet	2-Stroke	1994–1995	340975, 340976, 18-3673
Johnson/Evinrude	V4 Crossflow	90 Jet	2-Stroke	1994	340975, 340976, 18-3673
Johnson/Evinrude	V4 Crossflow	85	2-Stroke	1978–1980, 1993–1995	340975, 340976, 18-3673
Johnson/Evinrude	V4 Crossflow	88	2-Stroke	1984–1995	340975, 340976, 18-3673
Johnson/Evinrude	V4 Crossflow	90	2-Stroke	1983–1995	340975, 340976, 18-3673
Johnson/Evinrude	V4 Crossflow	100	2-Stroke	1979–1980, 1990–1995	340975, 340976, 18-3673
Johnson/Evinrude	V4 Crossflow	100 Commercial	2-Stroke	1984–1989	340975, 340976, 18-3673
Johnson/Evinrude	V4 Crossflow	110	2-Stroke	1985–1989	340975, 340976, 18-3673
Johnson/Evinrude	V4 Crossflow	112	2-Stroke	1994–1995	340975, 340976, 18-3673
Johnson/Evinrude	V4 Crossflow	115	2-Stroke	1978–1995	340975, 340976, 18-3673
Johnson/Evinrude	V4 Crossflow	140	2-Stroke	1978–1985	340975, 340976, 18-3673

Technical Specs

Product Type: Thermostat Kit with Hoses
Installation: Direct replacement
Fuel Type: Gasoline
Connection: Factory OEM fit for V4 Crossflow design
Housing Material: Aluminum, Plastic
Dimensions: 20.4 × 10.3 × 4.2 cm (8.03 × 4.06 × 1.65 inches) - package dimensions
Weight: 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

What’s in the Box

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

Installation Notes

Ensure the engine is off, cool, and the battery is disconnected.
Drain the cooling system to prevent spills.
Locate the thermostat housings and note the routing of the old hoses.
Remove the housing covers and carefully detach the old hoses.
Take out the old thermostats, gaskets, poppet valves, and related components.
Thoroughly clean the mating surfaces on the housings and covers.
Install the new poppet valves, springs, and grommets.
Place the new thermostats and gaskets into the housings, ensuring correct orientation.
Attach the new starboard and port hoses to their correct fittings.
Re-secure the housing covers, tightening bolts to the manufacturer's specified torque.
Refill the cooling system with the appropriate coolant.
Reconnect the battery, start the engine, and check for leaks and proper operating temperature.

Troubleshooting & FAQ

How do I know if this kit fits my engine?

This kit is specifically for Johnson/Evinrude V4 Crossflow engines from 65-140 HP, years 1978–1995. Please check the detailed 'Engine & Model Compatibility' table on this page to confirm your exact model and year.

What are the signs of a failing thermostat?

Common symptoms include engine overheating, running too cold at idle, inconsistent temperature gauge readings, or visible coolant leaks around the thermostat housing.

How often should I replace my thermostats and hoses?

It's recommended to inspect cooling system components annually. For saltwater use, consider replacement every 2-3 years as a preventative measure. For freshwater use, a 3-5 year interval is typical.

Is it necessary to replace hoses and thermostats at the same time?

Yes, this kit provides a complete service. Hoses degrade over time, and thermostats can stick open or closed. Replacing them together ensures all key components of the system are new and reliable.

My engine still overheats after installing the kit. What's wrong?

If overheating persists, check other cooling system parts. Inspect the water pump impeller, look for blockages in cooling passages, and verify the poppet relief valve is functioning correctly.

Are the hoses in this kit the same quality as OEM?

These hoses are manufactured to meet or exceed OEM specifications for fit, form, and function. They are made from durable materials designed to withstand the marine environment, providing a reliable alternative to original parts.

OEM vs. Aftermarket?

This listing is an aftermarket replacement (not OEM). Built to OEM-level specifications with comparable materials. Manufactured in an ISO 9002 facility, batch-inspected for consistency.

Shipping speed & cost

We ship worldwide quickly—typical transit 5–15 days. Standard shipping is free; expedited options appear at checkout where available.

Warranty & returns

Covered by a 1-year warranty against manufacturing defects under normal use. If issues arise, contact support with your order details. Returns are accepted within our standard window (unused & in original condition). See our policy page or reach out for instructions.

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.

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