Thermostat 170°F / 77°C – Fits MerCruiser 4.3L, 5.0L, 5.7L & 6.2L Engines (Replaces 864493)

Thermostat 170°F / 77°C – Fits MerCruiser 4.3L, 5.0L, 5.7L & 6.2L Engines (Replaces 864493)

This thermostat is engineered for MerCruiser 4.3L, 5.0L, 5.7L, and 6.2L MPI engines (V6 & V8) manufactured from 2000 to 2025. It is designed to maintain an optimal engine operating temperature of 170°F (77°C) in both fresh and saltwater applications.

As a direct replacement for multiple OEM and aftermarket parts, it ensures reliable performance for closed cooling systems with dry joint exhausts. This component is built to meet ISO9002 manufacturing standards for quality and durability.

• Regulates engine temperature at 170°F (77°C) for peak performance.
• Directly replaces Mercury 864493, Sierra 18-43015, and Mallory 9-43015.
• Package includes thermostat and rubber sealing ring for a complete 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. 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.

Technical Specifications

Package Contents

• 1 x Thermostat (Replaces 864493)
• 1 x Rubber sealing ring

Installation Guide

Always consult your service manual before performing maintenance. Professional installation is recommended.

1. Safety First: Ensure the engine is cool and disconnect the battery.
2. Drain Coolant: Partially drain the engine coolant to a level below the thermostat housing.
3. Locate Housing: Find the thermostat housing, typically where the main coolant hose connects to the engine.
4. Remove Housing: Loosen and remove the bolts securing the housing cover. Note their positions if they are different lengths.
5. Remove Old Thermostat: Lift out the old thermostat and the rubber sealing ring. Note the orientation of the thermostat.
6. Clean Surfaces: Thoroughly clean the mating surfaces of the housing and its cover, removing any old sealant or corrosion.
7. Install New Parts: Place the new rubber sealing ring in the groove and install the new thermostat in the same orientation as the old one.
8. Reassemble Housing: Re-place the housing cover and tighten the bolts to the manufacturer's specified torque.
9. Refill Coolant: Top off the cooling system with the appropriate coolant mixture.
10. Check for Leaks: Reconnect the battery, start the engine, and let it warm up. Carefully inspect for any coolant leaks around the housing.

Troubleshooting & FAQ

Q: How do I confirm this thermostat fits my MerCruiser engine?

A: The best way to ensure fitment is to check your engine's model and serial number against our compatible engine models table. Verifying that your existing part number matches one of the listed cross-references (e.g., 864493) also confirms compatibility.

Q: What are the signs of a failing thermostat?

A: Common signs of a bad thermostat include the engine overheating or running too cold (not reaching operating temperature), erratic temperature gauge readings, poor engine performance, and potential coolant leaks from the housing area.

Q: What is the operating temperature of this thermostat?

A: This thermostat is designed to maintain a consistent engine temperature of 170°F (77°C). This specific rating is critical for the performance and efficiency of the compatible MerCruiser engines.

Q: OEM vs. Aftermarket?

A: 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.

Q: How fast do you ship and how much does it cost?

A: 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.

Q: What is your warranty and return policy?

A: 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.