Thermostat Kit – Fits Mercury/Mariner 6-25 HP (Replaces 14586A3)

Product Details

This aftermarket Thermostat Kit (120°F/49°C) – Fits Mercury/Mariner 6-25 HP (Replaces 14586A3) is a complete service kit for Mercury and Mariner 2-stroke outboard engines from 6-25 HP. It is designed for various models, including the Sea Pro, Marathon, Super 15, and Viking series. Please confirm your engine's serial number with the compatibility chart below.

This kit provides a direct replacement for OEM part number Mercury 14586A3 and serves as a cross-reference for several other OEM and aftermarket parts, including Sierra 18-43052, GLM 13121, and Mallory 9-79805.

• Engineered for a direct-fit installation, matching OEM specifications.
• Helps maintain the correct engine operating temperature of 120°F (49°C).
• Includes the thermostat, gaskets, and other necessary components for a full replacement.

Part Number Matrix

Use this matrix to confirm equivalent references across OEM and aftermarket.

Engine & Model Compatibility

Confirm your engine model/year in the table below.

Fitment has been verified for the following Mercury/Mariner outboard engines. Always check your engine's serial number against the listed ranges to ensure an exact match.

Technical Specs

Product Type

Thermostat Kit

Thermostat Rating

120°F (49°C)

Application

Marine Outboard Cooling System

Compatibility

2-Stroke Outboard Motors

Package Type

Service Kit (Multiple Components)

OEM Standards

Meets Mercury Marine OEM specifications

Installation

Direct replacement

Operating Temperature

120°F (49°C) opening temperature

Warranty

Varies by manufacturer (OEM vs aftermarket)

What’s in the Box

• 1 x Thermostat (120°F/49°C) (14586)
• 1 x Grommet (64872)
• 1 x Coil Mounting Bracket To Block Gasket (66847)
• 1 x Diaphragm Screw (76451)
• 1 x Carrier, Poppet Valve (65848)
• 1 x Poppet (86596)
• 1 x Gasket (19205)
• 1 x Tank Cap Gasket (62386)
• 1 x Compression-Poppet Spring (66852)
• 1 x Diaphragm (64877)

Installation Notes

Always consult your engine's service manual before beginning work. The general steps for replacing a thermostat are:

1. Ensure the engine is cool and disconnect the battery.
2. Drain the engine coolant to a level below the thermostat housing.
3. Locate and remove the bolts securing the thermostat housing cover.
4. Remove the old thermostat, gaskets, and seals. Note the orientation of the thermostat.
5. Thoroughly clean the mating surfaces of the housing and cover, removing all old gasket material.
6. Install the new thermostat in the correct orientation, followed by the new gaskets and seals included in the kit.
7. Re-secure the housing cover, tightening bolts to the manufacturer's specified torque.
8. Refill the cooling system with the recommended coolant.
9. Reconnect the battery, start the engine, and let it reach operating temperature.
10. Carefully inspect the thermostat housing for any leaks.

Troubleshooting & FAQ

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.