Thermostat 71°C (159.8°F) – Fits Yanmar Marine 2GM/3GM Series (Replaces 121750-49800)

Thermostat 71°C (159.8°F) – Fits Yanmar Marine 2GM/3GM Series (Replaces 121750-49800)

This thermostat is designed for Yanmar's 2GM and 3GM series of small marine diesel engines, typically ranging from 8–30 HP. It ensures your engine maintains the correct operating temperature for optimal performance and efficiency.

This part is a direct replacement for the following OEM and aftermarket part numbers: Yanmar 121750-49800, Worldthump 121750-49800, Sogoparts 121750-49800, and ZDCBMDB 121750-49800.

• Rated Temperature: 71°C (159.8°F) opening temperature
• Installation: Direct replacement with no modification required
• Quality: OEM quality aftermarket part

Part Number Cross-Reference

Use this table to confirm equivalent part numbers across OEM and aftermarket brands.

Compatible Engine Models

Confirm your engine model/year in the table below.

Technical Specifications

Package Contents

1 x Thermostat (121750-49800)

Installation Guide

1. Ensure the engine is completely cool before starting.
2. Locate the thermostat housing on the engine block. It's usually where the main coolant hose connects.
3. Place a drain pan underneath to catch any spilled coolant.
4. Carefully remove the bolts securing the thermostat housing cover.
5. Lift the cover and remove the old thermostat. Note its orientation.
6. Clean the mating surfaces of the housing and cover, removing any old gasket material.
7. Install the new thermostat in the same orientation as the old one.
8. Place a new gasket (if required, sold separately) and reinstall the housing cover.
9. Tighten the bolts to the manufacturer's specified torque. Do not overtighten.
10. Refill the cooling system with the appropriate coolant.
11. Start the engine and check for leaks around the housing as it comes up to temperature.

Troubleshooting & FAQ

How do I confirm this part fits my engine?
Cross-reference your engine's original thermostat part number with the numbers listed in the "Part Number Cross-Reference" table. Also, verify your engine model is included in the "Compatible Engine Models" list.

What are the signs of a bad thermostat?
Common symptoms include engine overheating, running too cold (not reaching operating temperature), erratic temperature gauge readings, and potential coolant leaks from the housing.

How often should I replace my marine engine's thermostat?
While there is no fixed interval, it is good practice to inspect it during regular cooling system service or replace it proactively every few years, especially if operating in saltwater.

OEM vs. Aftermarket?
This listing is an aftermarket replacement part (not an OEM component). We build to OEM specifications using comparable-grade materials. Production is done in an ISO9002-certified facility, and each batch is inspected for consistent performance.

How fast do you ship and how much does it cost?
We offer fast global shipping—typically 5–15 days worldwide—and standard shipping is free. Expedited options are available at checkout depending on your location.

What is your warranty and return policy?
This product includes a 1-year warranty against manufacturing defects under normal use. If something goes wrong, contact our support team with your order details. Returns are accepted within our standard return window (unused & in original condition); please see our policy page or reach out for instructions.

Important Notes

• Verify that the product images and specifications match your original part. If discrepancies exist—even if your model is listed—do not proceed with the purchase.
• This product is an aftermarket replacement part and is not an OEM component.
• Professional installation is recommended to ensure safety and optimal performance.

Why Choose JLM MARINE?

• Quality Assured: As a trusted manufacturer for over 20 years, we supply top marine brands globally.
• Fast Global Shipping: Free delivery worldwide in 5–15 days.
• Direct from Manufacturer: Competitive pricing without compromising quality.