Thermostat 170°F / 77°C – Fits MerCruiser 4.3L, 5.0L, 5.7L & 6.2L Engines (Replaces Mercury 864493)
Thermostat 170°F / 77°C – Fits MerCruiser 4.3L, 5.0L, 5.7L & 6.2L Engines (Replaces Mercury 864493) is backordered and will ship as soon as it is back in stock.
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Delivery and Shipping
Delivery and Shipping
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Thermostat 170°F / 77°C – Fits MerCruiser 4.3L, 5.0L, 5.7L & 6....
Thermostat 170°F / 77°C – Fits MerCruiser 4.3L, 5.0L, 5.7L & 6.2L Engines (Replaces Mercury 864493) is backordered and will ship as soon as it is back in stock.
Product Details
This is a direct-replacement Thermostat 170°F / 77°C – Fits MerCruiser 4.3L, 5.0L, 5.7L & 6.2L Engines (Replaces 864493). It is designed for a wide range of MerCruiser V6 and V8 MPI sterndrive engines manufactured from 2000 to 2025, ensuring proper engine operating temperature for optimal performance and fuel efficiency.
It serves as a direct interchange for multiple part numbers, including Mercury 864493, Sierra 18-43015, Mallory 9-43015, and Quicksilver 864493.
- Engineered for use in both fresh and salt water cooling systems.
- Installation is straightforward, requiring only the removal of the thermostat housing.
- Package includes the thermostat and a new rubber sealing ring for a complete replacement.
Part Number Matrix
Use this matrix to confirm equivalent references across OEM and aftermarket.
| Brand | Part Number |
|---|---|
| Mercury | 864493 |
| Mercury | 25-807134 |
| Sierra | 18-43015 |
| Mallory | 9-43015 |
| Quicksilver | 864493 |
Engine & Model Compatibility
Confirm your engine model/year in the table below.
This thermostat fits the specified MerCruiser sterndrive models. Pay close attention to serial number ranges to ensure correct fitment.
| Brand | Model | Rated HP | Stroke | Years | OEM Part No. | Notes |
|---|---|---|---|---|---|---|
| MerCruiser | 4.3L Alpha/Bravo | V6 | 4-Stroke | 2000–2025 | 864493 | Serial numbers 1A030370 and up |
| MerCruiser | 5.0L Alpha/Bravo | V8 | 4-Stroke | 2000–2025 | 864493 | Serial numbers 0W060000 and up |
| MerCruiser | 5.7L Alpha/Bravo | V8 | 4-Stroke | 2000–2025 | 864493 | Serial numbers 1A090000 and up |
| MerCruiser | 6.2L Alpha/Bravo | V8 | 4-Stroke | 2000–2025 | 864493 | Serial numbers 0W310000 and up |
| MerCruiser | 4.3L MPI Alpha/Bravo | V6 | 4-Stroke | 2000–2025 | 864493 | Serial numbers 1A030370 and up |
| MerCruiser | 4.3L MPI Alpha/Bravo EC | V6 | 4-Stroke | 2000–2025 | 864493 | Serial numbers 1A637496 and up |
| MerCruiser | 4.5L MPI 200 Alpha/Bravo | V6 | 4-Stroke | 2000–2025 | 864493 | Serial numbers 2A441953 and up |
| MerCruiser | 4.5L MPI 200 Alpha/Bravo EC | V6 | 4-Stroke | 2000–2025 | 864493 | Serial numbers 2A441953 and up |
| MerCruiser | 4.5L MPI 250 Alpha/Bravo | V6 | 4-Stroke | 2000–2025 | 864493 | Serial numbers 2A441953 and up |
| MerCruiser | 4.5L MPI 250 Alpha/Bravo EC | V6 | 4-Stroke | 2000–2025 | 864493 | Serial numbers 2A441953 and up |
| MerCruiser | 5.0L MPI Alpha/Bravo | V8 | 4-Stroke | 2000–2025 | 864493 | Serial numbers 0M600000 and up |
| MerCruiser | 5.0L MPI Alpha/Bravo EC | V8 | 4-Stroke | 2000–2025 | 864493 | Serial numbers 1A300000 and up |
| MerCruiser | 350 MAG MPI Alpha/Bravo | 5.7L V8 | 4-Stroke | 2000–2025 | 864493 | Serial numbers 0M600000 and up |
| MerCruiser | 350 MAG MPI Alpha/Bravo EC | 5.7L V8 | 4-Stroke | 2000–2025 | 864493 | Serial numbers 1A300000 and up |
| MerCruiser | 5.7L MPI Horizon MIE | V8 | 4-Stroke | 2000–2025 | 864493 | Serial numbers 1A090000 and up |
| MerCruiser | 5.7L MPI MIE | V8 | 4-Stroke | 2000–2025 | 864493 | Serial numbers 1A090000 and up |
| MerCruiser | 5.7L MPI MIE EC | V8 | 4-Stroke | 2000–2025 | 864493 | Serial numbers 1A090000 and up |
| MerCruiser | 6.2L MPI Horizon MIE | V8 | 4-Stroke | 2000–2025 | 864493 | Serial numbers 1A090000 and up |
| MerCruiser | 6.2L MPI MIE | V8 | 4-Stroke | 2000–2025 | 864493 | Serial numbers 1A090000 and up |
| MerCruiser | 6.2L MPI MIE EC | V8 | 4-Stroke | 2000–2025 | 864493 | Serial numbers 1A091600 and up |
Technical Specs
- Product Type
- Engine Thermostat
- Installation
- Direct replacement, requires thermostat housing removal
- Temperature Rating
- 77°C (170°F)
- Housing Material
- Stainless steel
- Applications
- Fresh and salt water cooling systems
- Compatible Cooling
- Closed cooling systems with dry joint exhaust
- Package Includes
- Thermostat and rubber sealing ring
- Warranty
- Manufacturer standard warranty
- Production Standard
- ISO9002 certified manufacturing
What’s in the Box
- 1 x Thermostat (864493)
- 1 x Rubber sealing ring
Installation Notes
- Ensure the engine is completely cool before starting work.
- Drain the engine coolant to a level below the thermostat housing.
- Locate and carefully remove the bolts securing the thermostat housing.
- Note the orientation of the old thermostat before removing it from the housing.
- Thoroughly clean the mating surfaces of the housing and the engine block.
- Install the new thermostat and rubber sealing ring in the correct orientation.
- Re-install the housing cover and tighten the bolts to the manufacturer's specified torque.
- Refill the cooling system with the appropriate coolant.
- Start the engine, check for any leaks around the housing, and monitor the temperature gauge to ensure normal operation.
Troubleshooting & FAQ
How do I know if my thermostat is failing?
Common signs of a faulty thermostat include engine overheating, the engine not reaching its normal operating temperature (running too cool), or erratic and sudden changes in the temperature gauge reading.
Is this the correct temperature rating for my engine?
This is a 170°F (77°C) thermostat, which is the standard OEM-specified temperature for the listed MerCruiser models. Using the correct temperature is critical for engine performance, fuel economy, and longevity.
How can I be certain this part fits my specific engine?
Verify that your engine model and year are listed in our compatibility table. Most importantly, check that your engine's serial number falls within the specified range for your model. Cross-referencing the OEM part number (864493) with your service manual or the old part itself is the best way to guarantee a match.
What is included in this kit?
The package contains one thermostat and the required rubber sealing ring. This ensures you have the necessary components for a correct seal and complete installation.
How often should a marine thermostat be replaced?
As a preventative maintenance item, it is good practice to inspect the thermostat annually and consider replacement every 2-3 years, especially if operating in saltwater. It should be replaced immediately if you notice any signs of failure.
Is this an OEM or aftermarket part?
This listing is for a high-quality aftermarket replacement part, not an OEM component. It is built to meet or exceed OEM-level specifications using comparable materials and is manufactured in an ISO 9002 certified facility, with batch inspections for quality and consistency.
How fast is shipping?
We ship worldwide quickly, with typical transit times of 5–15 days for most regions. Standard shipping is free, and expedited options will appear at checkout if they are available for your location.
What is the warranty and return policy?
This product is covered by a 1-year warranty against manufacturing defects under normal use conditions. Should an issue arise, contact our support team with your order details. Returns are accepted within our standard window for items that are unused and in their original condition. Please see our full 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.
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