Thermostat – Fits Honda Marine 8-225 HP (Replaces 19300-ZW9-003, 19300-ZY3-023)

Thermostat – Fits Honda Marine 8-225 HP (Replaces 19300-ZW9-003, 19300-ZY3-023)

This stainless steel thermostat is designed for Honda Marine 4-stroke outboard engines from 8 HP to 225 HP (years 1998–present). It maintains proper engine operating temperature by regulating coolant flow to ensure optimal performance and prevent overheating.

Direct Replacements: Honda 19300-ZW9-003, 19300-ZY3-023, 19300ZY3023, 19300ZW9003, Sierra 18-3628, Sierra 18-3541.

• Durable Construction: Made from high-quality stainless steel and copper with an NBR rubber seal for excellent heat, corrosion, and oil resistance.
• Precise Temperature Control: Engineered to open at 60°C (140°F) to maintain stable engine operating temperatures.
• Complete Kit: Includes one thermostat and two new seals for a comprehensive installation.

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 (19300-ZW9-003)
• 2 x Thermostat Seals (19302-921-003)

Installation Guide

1. Disconnect the Battery: Ensure the engine is off and cool, then disconnect the negative battery terminal for safety.
2. Drain Coolant: Place a container under the engine and partially drain the cooling system to a level below the thermostat housing.
3. Access the Housing: Locate and remove the bolts securing the thermostat housing cover.
4. Remove Old Parts: Carefully take out the old thermostat and its associated seals or gaskets. Note their orientation.
5. Clean Surfaces: Thoroughly clean the thermostat housing and cover surfaces, removing any old gasket material or corrosion.
6. Install New Thermostat: Place the new thermostat into the housing in the correct orientation, followed by the new seals.
7. Reassemble: Secure the housing cover and tighten the bolts to the manufacturer's recommended torque specification.
8. Refill and Check: Refill the cooling system, reconnect the battery, and start the engine. Check for any leaks around the housing and monitor the temperature gauge to ensure normal operation.

Troubleshooting & FAQ

How do I confirm this thermostat fits my Honda engine?
This thermostat fits most Honda Marine 4-stroke outboards from 8 HP to 225 HP (1998–Present). To be certain, please check the "Compatible Engine Models" table on this page and compare the OEM part numbers (19300-ZW9-003, 19300-ZY3-023) with those listed in your engine's service manual.

What are the signs of a failing thermostat?
Common signs include the engine overheating, running too cold (not reaching proper operating temperature), erratic temperature gauge readings, or visible coolant leaks around the thermostat housing.

What is the opening temperature of this thermostat?
This thermostat is calibrated to begin opening at 60°C (140°F) to properly regulate the engine's operating temperature.

What materials is this thermostat made from?
It is constructed from a combination of stainless steel and copper for durability and corrosion resistance. It also includes an NBR rubber seal, which is known for its high resistance to heat, oil, and abrasion.

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.