Mercury Mariner Outboard Thermostat 120°F – 6, 7, 8, 9.9 & 15 HP – Replaces 14586
Mercury Mariner Outboard Thermostat 120°F – 6, 7, 8, 9.9 & 15 HP – Replaces 14586 is backordered and will ship as soon as it is back in stock.
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Delivery and Shipping
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Mercury Mariner Outboard Thermostat 120°F – 6, 7, 8, 9.9 & 15 H...
Mercury Mariner Outboard Thermostat 120°F – 6, 7, 8, 9.9 & 15 HP – Replaces 14586 is backordered and will ship as soon as it is back in stock.
Product Details
This is an aftermarket replacement outboard thermostat for selected Mercury Mariner outboard applications. It is rated to open at 120°F (49°C) and is listed for Mercury Mariner 6, 7, 8, 9.9, and 15 HP engines with the applicable HPA197112 and later serial range. Always compare the required part number and serial-number range with your engine before ordering.
This thermostat replaces Mercury Marine OEM part numbers 14586 and 14586A3. It is also identified as a replacement for Sierra 18-3549. Part-number references apply only where the original engine application and temperature rating match.
- Product Type: Replacement outboard engine thermostat.
- Opening Temperature: 120°F (49°C).
- Installation: Direct replacement when the original thermostat and part-number application match.
- Application: Selected Mercury Mariner 6, 7, 8, 9.9, and 15 HP outboards, HPA197112 and later.
Part Number References
Use the following references to help compare the thermostat with the part removed from your engine. These numbers do not replace model, serial-number, and temperature-rating verification.
| Brand | Part Number | Reference |
|---|---|---|
| Mercury Marine | 14586 | OEM replacement reference |
| Mercury Marine | 14586A3 | OEM replacement reference |
| Sierra | 18-3549 | Aftermarket reference |
Engine Compatibility
The company application record identifies this thermostat for the following Mercury Mariner horsepower groups with the applicable HPA197112 and later serial range:
| Brand | Engine Family | Rated HP | Serial Condition | Thermostat Reference |
|---|---|---|---|---|
| Mercury Mariner | Outboard | 6 HP | HPA197112 and later | 14586 / 14586A3 |
| Mercury Mariner | Outboard | 7 HP | HPA197112 and later | 14586 / 14586A3 |
| Mercury Mariner | Outboard | 8 HP | HPA197112 and later | 14586 / 14586A3 |
| Mercury Mariner | Outboard | 9.9 HP | HPA197112 and later | 14586 / 14586A3 |
| Mercury Mariner | Outboard | 15 HP | HPA197112 and later | 14586 / 14586A3 |
Some catalog references also associate this thermostat family with additional Mercury and Mariner applications. Because fitment varies by model configuration and serial range, do not rely on horsepower alone; confirm the exact engine model, serial number, required thermostat temperature, and original part number before installation.
Technical Specifications
- Product Type
- Outboard engine thermostat
- Operating Rating
- 120°F (49°C) opening temperature
- Installation
- Direct replacement for matching applications
- OEM References
- Mercury Marine 14586 and 14586A3
- Aftermarket Reference
- Sierra 18-3549
- Application
- Selected Mercury Mariner 6, 7, 8, 9.9, and 15 HP outboards with HPA197112 and later serial condition
What's in the Box
- 1 x 120°F outboard thermostat
This listing is for the thermostat only. The company record identifies the product as a single thermostat rather than a multi-component kit. Gaskets, seals, housing parts, or other installation components should be confirmed separately for your specific engine.
Installation Notes
- Confirm the engine model, serial number, thermostat temperature, and original part number before beginning work.
- Allow the engine to cool completely and disconnect the battery according to the engine manufacturer's safety procedure.
- Locate the thermostat housing and remove the cover carefully, keeping track of the fasteners and the original thermostat orientation.
- Remove the old thermostat and any sealing material, then clean the mating surfaces without damaging the housing.
- Install the replacement thermostat in the same orientation as the original part.
- Install a new gasket or seal if required for your engine application. Gaskets and seals are not identified as included with this single-thermostat listing.
- Reinstall the housing cover and tighten the fasteners to the engine manufacturer's specified torque.
- Run the engine using the correct water-supply procedure for your outboard and check for proper water flow, leaks, and normal operating temperature.
Troubleshooting & FAQ
How do I know if my thermostat may be failing?
Possible symptoms include abnormal operating temperature, overheating, poor temperature control, or an engine that does not reach its normal operating temperature. These symptoms can also be caused by restricted water passages, a damaged water pump, incorrect installation, or other cooling-system problems.
Is a gasket included?
This product is identified by the company record as a single thermostat, not a multi-component kit. A gasket or seal is not identified as included, so confirm the required sealing parts for your exact engine before ordering.
Will this fit my Mercury Mariner engine?
It is listed for selected Mercury Mariner 6, 7, 8, 9.9, and 15 HP applications with the applicable HPA197112 and later serial condition. Verify the complete model and serial number, the 120°F rating, and the original thermostat reference before purchase.
Does this fit Johnson or Evinrude engines?
Johnson and Evinrude fitment is not established for this product record. Do not use the listed Mercury and Mariner references to select a thermostat for a Johnson or Evinrude engine.
Is this an OEM thermostat?
No. This is an aftermarket replacement thermostat intended to replace the listed Mercury Marine references in matching applications.
What should I verify before ordering?
Compare the original thermostat, part number, opening temperature, engine model, horsepower, and full serial-number range. If any of these details do not match, confirm compatibility with a qualified marine technician before ordering.
Safety & Important Information
- Allow the engine to cool completely before removing the thermostat housing.
- Use the correct water-supply and starting procedure for your outboard during testing.
- Do not operate the engine if the cooling system has inadequate water flow or leaks.
- Verify the part number, 120°F rating, engine model, and serial-number condition before installation.
- Professional marine-service installation is recommended when the correct application or installation procedure is uncertain.
About Sea Sierra
- Marine Parts Support — We provide replacement components for a range of marine maintenance and repair applications.
- Application-Focused Listings — Product references and fitment details are provided to help you compare the replacement part with your original component.
- Support When Needed — If your engine model, serial number, or original part differs from the information shown here, confirm compatibility before ordering.
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