Thermostat Housing Gasket – Fits Yanmar 1GM, 2GM, 3GM Marine Engines (Replaces 121450-44411)
Thermostat Housing Gasket – Fits Yanmar 1GM, 2GM, 3GM Marine Engines (Replaces 121450-44411) 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 Housing Gasket – Fits Yanmar 1GM, 2GM, 3GM Marine Engine...
Product Details
This high-temperature Thermostat Housing Gasket – Fits Yanmar 1GM, 2GM, 3GM Marine Engines creates a reliable seal for the engine cooling system. It is designed for a wide range of Yanmar marine diesel engines, including the GM/HM series built from 1980 to 1983 and the GM/HM Bored Up series from 1983 to present.
This part is a direct replacement for Yanmar OEM part numbers 121450-44410 and 121450-44411.
- Installs in the engine cooling system to prevent leaks.
- Engineered for marine diesel engine environments.
- Ensures a secure seal for the thermostat housing.
Part Number Matrix
Use this matrix to confirm equivalent references across OEM and aftermarket.
| Brand | Part Number | Superseded By |
|---|---|---|
| Yanmar | 121450-44410 | 121450-44411 |
Engine & Model Compatibility
Confirm your engine model/year in the table below.
Fitment includes Yanmar GM/HM series (1980–2005+) 4-stroke diesel engines from 7.5 to 30 HP, covering both raw water and fresh water cooled models.
| Brand | Model | Rated HP | Stroke | Years | OEM Part No. | Notes |
|---|---|---|---|---|---|---|
| Yanmar | 1GM | 7.5 | 4-Stroke | 1980–1983 | 121450-44411 | Raw water cooled |
| Yanmar | 1GM10 | 9 | 4-Stroke | 1983–2009 | 121450-44411 | Raw water cooled |
| Yanmar | 2GM | 15 | 4-Stroke | 1980–1983 | 121450-44411 | Raw water cooled |
| Yanmar | 2GM20 | 18 | 4-Stroke | 1983–2005 | 121450-44411 | Raw water cooled |
| Yanmar | 2GM20F | 18 | 4-Stroke | 1983–2005 | 121450-44411 | Fresh water cooled |
| Yanmar | 2GM20-YEU | 18 | 4-Stroke | 1997–Present | 121450-44411 | European manufactured |
| Yanmar | 3GM | 22.5 | 4-Stroke | 1980–1983 | 121450-44411 | Raw water cooled |
| Yanmar | 3GM30 | 27 | 4-Stroke | 1983–2005 | 121450-44411 | Raw water cooled |
| Yanmar | 3GM30F | 27 | 4-Stroke | 1983–2005 | 121450-44411 | Fresh water cooled |
Technical Specs
- Product Type
- Thermostat Housing Gasket
- Installation
- Engine Cooling System
- Fuel Type
- Diesel
- Housing Material
- High-Temperature Gasket Material
- Dimensions
- 10.5" L x 6.5" W x 0.1" H
- Other Technical Attributes
- Designed for marine diesel engines
What’s in the Box
- 1 x Thermostat Housing Gasket (Replaces 121450-44410/121450-44411)
Installation Notes
- Allow the engine to cool completely and disconnect the battery.
- Drain coolant to a level below the thermostat housing.
- Unbolt and remove the thermostat housing cover.
- Carefully take out the old gasket and thermostat. Thoroughly clean any residue from the housing and cover surfaces.
- Position the new gasket correctly on the housing.
- Reinstall the cover and tighten the bolts to the manufacturer's recommended torque specifications.
- Refill the cooling system, reconnect the battery, and run the engine to check for leaks.
Troubleshooting & FAQ
What are the signs of a failing thermostat gasket?
Common signs include visible coolant leaks around the thermostat housing, engine overheating, and frequent low coolant levels. A visual inspection may reveal a brittle, cracked, or degraded gasket.
How can I be sure this gasket fits my engine?
This gasket is compatible with the Yanmar 1GM, 2GM, and 3GM series engines listed in the compatibility table. The most reliable method is to match the OEM part number 121450-44411 to your engine's service manual.
What is the recommended replacement interval for this gasket?
It is best practice to replace the thermostat housing gasket whenever you replace the thermostat or service the cooling system. There is no fixed interval, but it should be inspected during routine maintenance.
Is this gasket suitable for both raw water and fresh water cooled engines?
Yes, as shown in the compatibility table, this gasket fits both raw water (e.g., 2GM20) and fresh water cooled (e.g., 2GM20F) versions of the specified Yanmar engines.
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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