Thermostat Kit – Fits Johnson Evinrude V4 Crossflow 65-140HP (Replaces 18-3673, 340975, 340976)
Thermostat Kit – Fits Johnson Evinrude V4 Crossflow 65-140HP (Replaces 18-3673, 340975, 340976) is backordered and will ship as soon as it is back in stock.
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Delivery and Shipping
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Thermostat Kit – Fits Johnson Evinrude V4 Crossflow 65-140HP (Repla...
Thermostat Kit – Fits Johnson Evinrude V4 Crossflow 65-140HP (Replaces 18-3673, 340975, 340976) is backordered and will ship as soon as it is back in stock.
Product Details
This Thermostat Kit with Hoses – Fits Johnson Evinrude V4 Crossflow 65-140HP is a complete direct replacement solution for Johnson and Evinrude V4 Crossflow outboard engines manufactured between 1978 and 1995. It is engineered to restore proper engine operating temperature for models including 65 & 80 Jet, 85HP, 88HP, 90HP, 100HP, 110HP, 112HP, 115HP, and 140HP.
The kit serves as a direct interchange for Sierra 18-3673, GLM 13270, OMC 434841, and Johnson/Evinrude part numbers 340975 and 340976.
- Includes a 143°F (62°C) rated thermostat for optimal engine performance.
- Comes as a complete kit with both starboard and port hoses for a full replacement.
- Designed for direct, factory-style installation with OEM-fit fittings.
Part Number Matrix
Use this matrix to confirm equivalent references across OEM and aftermarket.
| Brand | Part Number |
|---|---|
| Sierra | 18-3673 |
| GLM | 13270 |
| OMC | 434841 |
| Johnson/Evinrude | 340975 |
| Johnson/Evinrude | 340976 |
| Johnson/Evinrude | 18-3673 |
Engine & Model Compatibility
Confirm your engine model/year in the table below.
This kit is designed exclusively for the Johnson and Evinrude V4 Crossflow models listed.
| 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
- Fitting Type
- OEM-style fittings
- Operating Temperature
- 143°F (62°C) thermostat rating
- Other Technical Attributes
- Complete kit with starboard and port hoses
What’s in the Box
- 1 x Thermostat (393659/434841/378065/508626/5005440)
- 1 x Gasket (332369/18-0977)
- 1 x Thermostat Gasket (321932/18-0675)
- 1 x Poppet Relief Valve (318395/18-3564)
- 1 x Grommet (321692/18-2391)
- 1 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 completely cool and disconnect the battery.
- Drain the engine cooling system to minimize fluid loss.
- Locate and unbolt the thermostat housing cover. Note the orientation of existing parts.
- Remove the old thermostat, gaskets, valve components, and hoses.
- Thoroughly clean all mating surfaces of the housing and cover, removing any old gasket material.
- Install the new poppet valve, spring, grommet, and thermostat into the housing.
- Place the new gaskets correctly and attach the new starboard and port hoses, securing clamps tightly.
- Re-secure the housing cover, tightening bolts evenly to the manufacturer's specified torque.
- Refill the cooling system, reconnect the battery, and start the engine, checking carefully for any leaks.
Troubleshooting & FAQ
How do I know if my thermostat has failed?
Common signs include the engine overheating, running too cold (not reaching operating temperature), erratic temperature gauge readings, or visible coolant leaks around the thermostat housing.
Will this kit fit my specific Johnson/Evinrude V4 model?
This kit is designed for V4 Crossflow engines from 1978–1995. It is critical to check the compatibility table on this page to confirm your exact model, horsepower, and year range before purchasing.
What is the purpose of the poppet relief valve?
The poppet valve regulates engine temperature at higher RPMs. It allows excess water pressure to bypass the thermostat, ensuring sufficient cooling under load and preventing overheating.
Is it necessary to replace hoses and the thermostat at the same time?
Yes, this kit includes both because hoses can degrade and become brittle at a similar rate as internal thermostat components. Replacing them together prevents future leaks and ensures the cooling system's integrity.
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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