Thermostat (60°C/140°F) – Fits Honda, Mercury, Yamaha 8-255 HP (Replaces 19300-ZY3-023, 19300-ZW9-003)

Thermostat (60°C/140°F) – Fits Honda, Mercury, & Yamaha 4-Stroke Outboards

This aftermarket thermostat is a high-quality replacement for a wide range of Honda, Mercury, and Yamaha 4-stroke outboard engines. It is engineered to meet or exceed OEM specifications, ensuring reliable engine temperature regulation for optimal performance and longevity. This part is designed for Honda 8-225 HP (2001-Present), Mercury 15-90 HP, and Yamaha 9.9-70 HP (1987-Present) models.

This component is a direct replacement for numerous Honda, Mercury, Yamaha, and Sierra part numbers, making it a versatile and reliable choice for maintenance and repair.

• Operating Temperature: Opens at a factory-set 60°C (140°F).
• Installation Type: Direct replacement for the original OEM thermostat.
• Construction: Built with an OEM-grade brass and rubber composite for durability and corrosion resistance.

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.

For Mercury owners, here’s a guide to help you identify your engine’s serial/model: Mercury Serial Number Guide. You can also review exploded diagrams to verify part numbers: Mercury Parts Diagrams & Catalog.

For Yamaha owners, here’s a guide to help you identify your engine’s serial/model: Yamaha Serial Number Guide. You can also review exploded diagrams to verify part numbers: Yamaha Parts Diagrams & Catalog.

Honda

Mercury

Yamaha

Technical Specifications

Package Contents

1 x Thermostat Assembly (60°C/140°F rating)

Installation Guide

1. Safety First: Ensure the engine is completely cool and disconnected from the power source before beginning.
2. Locate Thermostat Housing: Find the thermostat housing on the engine block, typically near the top of the cylinder head where the main coolant hose connects.
3. Drain Coolant: Place a suitable container underneath and drain enough coolant to bring the level below the thermostat housing. This prevents spills.
4. Remove Housing Cover: Loosen and remove the bolts holding the thermostat housing cover in place. Take note of their placement for easier reassembly.
5. Extract Old Thermostat: Carefully lift out the old thermostat and its gasket or seal. Thoroughly clean any old gasket material or corrosion from both the housing and cover surfaces.
6. Install New Thermostat: Position the new thermostat assembly in the housing, ensuring it is correctly oriented. The integrated seal should sit flush.
7. Re-secure Cover: Replace the housing cover and tighten the bolts evenly in a crisscross pattern to the manufacturer's specified torque.
8. Refill Coolant: Top off the cooling system with the manufacturer-recommended coolant.
9. Check for Leaks: Start the engine and let it warm up, carefully inspecting the thermostat housing for any signs of coolant leaks.

Troubleshooting & FAQ

How do I confirm this thermostat fits my specific engine model?

Check the "Compatible Engine Models" and "Part Number Cross-Reference" tables on this page. It is crucial to match your engine's brand, model, HP, and year with the provided data. For Mercury and Yamaha engines, we’ve included links to serial number guides and parts catalogs to help you verify the correct OEM part number.

What are the common signs of a failing thermostat?

Common signs include the engine overheating, the engine taking too long to reach its normal operating temperature, or erratic temperature gauge readings. A thermostat stuck open will prevent the engine from warming up properly, while one stuck closed will cause it to overheat.

Does this thermostat require a separate gasket?

This thermostat is a complete assembly that includes an integrated rubber seal, just like the OEM version. No separate gasket is typically required. However, you should always inspect the mating surfaces of the housing for flatness and damage before installation.

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.