Thermostat 71°C – Fits Yanmar Marine 2GM/3GM Series (Replaces 121750-49800)
Thermostat 71°C – Fits Yanmar Marine 2GM/3GM Series (Replaces 121750-49800) is backordered and will ship as soon as it is back in stock.
Couldn't load pickup availability
Worry-free returns
Worry-free returns
You may return most new, unopened items within 7 days of delivery for a full refund. We'll also pay the return shipping costs if the return is a result of our error (you received an incorrect or defective item, etc.).
You should expect to receive your refund within four weeks of giving your package to the return shipper, however, in many cases you will receive a refund more quickly. This time period includes the transit time for us to receive your return from the shipper (5 to 10 business days), the time it takes us to process your return once we receive it (3 to 5 business days), and the time it takes your bank to process our refund request (5 to 10 business days).
If you need to return an item, simply login to your account, view the order using the "Complete Orders" link under the My Account menu and click the Return Item(s) button. We'll notify you via e-mail of your refund once we've received and processed the returned item.
Delivery and Shipping
Delivery and Shipping
Free standard shipping on all orders under 1 KG
Thermostat 71°C – Fits Yanmar Marine 2GM/3GM Series (Replaces 12175...
Product Details
This genuine-quality Thermostat 71°C (159.8°F) – Fits Yanmar Marine 2GM/3GM Series is designed as a direct replacement for small Yanmar marine diesel engines. It is engineered for models in the 2GM and 3GM series, which are typically 8–30 HP, 4-stroke engines manufactured through the mid-2000s, ensuring proper engine cooling performance.
This part directly replaces Yanmar P/N 121750-49800 and is also referenced by aftermarket numbers from Worldthump, Sogoparts, and ZDCBMDB.
- Engineered for direct replacement with no modification required.
- Maintains a rated opening temperature of 71°C (159.8°F).
- Meets or exceeds OEM quality standards for reliable performance.
Part Number Matrix
Use this matrix to confirm equivalent references across OEM and aftermarket.
| Brand | Part Number |
|---|---|
| Yanmar | 121750-49800 |
| Worldthump | 121750-49800 |
| Sogoparts | 121750-49800 |
| ZDCBMDB | 121750-49800 |
Engine & Model Compatibility
Confirm your engine model/year in the table below.
Designed specifically for Yanmar marine diesel engines, this thermostat ensures a precise fit for the models listed.
| Brand | Model | Rated HP | Stroke | OEM Part No. |
|---|---|---|---|---|
| Yanmar | 2GM20F | 20 | 4-Stroke | 121750-49800 |
| Yanmar | 2GM20F-YEU | 20 | 4-Stroke | 121750-49800 |
| Yanmar | 2GMF | 4-Stroke | 121750-49800 | |
| Yanmar | 3GM30F | 30 | 4-Stroke | 121750-49800 |
| Yanmar | 3GM30F-YEU | 30 | 4-Stroke | 121750-49800 |
| Yanmar | 3GMDF | 4-Stroke | 121750-49800 | |
| Yanmar | 3GMF | 4-Stroke | 121750-49800 | |
| Yanmar | 3HM35F | 35 | 4-Stroke | 121750-49800 |
| Yanmar | 3HMF | 4-Stroke | 121750-49800 |
Technical Specs
- Product Type
- Thermostat
- Installation
- Direct replacement, no modification required
- Rated Temperature
- 71°C (159.8°F)
- Connection
- Direct fit to thermostat housing
- Housing Material
- Metal
- Dimensions
- Compact design for marine application
- Operating Temperature
- 71°C (159.8°F) opening temperature
- Warranty
- Varies by seller: 30-day to 6-month warranty
- Other Technical Attributes
- OEM quality replacement part
What’s in the Box
- 1 x Thermostat (121750-49800)
Installation Notes
- Disconnect the battery to ensure safety.
- Allow the engine to cool completely and drain the coolant into a suitable container.
- Locate and remove the thermostat housing cover.
- Remove the old thermostat and gasket, taking note of its orientation.
- Thoroughly clean the mating surfaces of the housing and cover.
- Install the new thermostat in the correct orientation.
- Reinstall the housing cover with a new gasket if required.
- Refill the cooling system with the recommended coolant type.
- Reconnect the battery, start the engine, and check for leaks as it warms up.
Troubleshooting & FAQ
How do I confirm this thermostat fits my engine?
This thermostat is for Yanmar 2GM and 3GM series engines. Please check the "Engine & Model Compatibility" table and match your specific model (e.g., 2GM20F, 3GM30F). Always verify the OEM part number 121750-49800 against your service manual.
What temperature does this thermostat open at?
This thermostat is rated to begin opening at 71°C (159.8°F), ensuring your engine operates within its ideal temperature range for efficiency and longevity.
What are the signs of a failing thermostat?
Common signs include engine overheating (stuck closed) or running too cool and failing to reach operating temperature (stuck open). You may also notice erratic temperature gauge readings or coolant leaks around the housing.
How often should a marine engine thermostat be replaced?
While there is no fixed interval, it is good practice to inspect the thermostat during routine cooling system service (e.g., every 2-3 years or as recommended by your engine manual) and replace it if corrosion or failure is suspected.
Is this an OEM part?
This listing is an aftermarket replacement (not OEM). It is built to OEM-level specifications with comparable materials and manufactured in an ISO 9002 facility, then batch-inspected for consistency.
How fast do you ship?
We ship worldwide quickly—typical transit is 5–15 days. Standard shipping is free; expedited options appear at checkout where available.
What is the warranty policy?
This product is 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 if the item is unused and in its 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.
Payment & Security
Payment methods
Your payment information is processed securely. We do not store credit card details nor have access to your credit card information.
