Mercury Mariner Thermostat Kit (120°) – Fits Mercury/Mariner Outboards 6-25 HP (Replaces 14586A3)

Mercury Mariner Thermostat Kit (120°) – Fits Mercury/Mariner Outboards 6-25 HP (Replaces 14586A3)

This thermostat kit is designed for a wide range of Mercury and Mariner 2-stroke outboard engines, including models from 6 HP to 25 HP manufactured between 1984 and 1998. It ensures your engine maintains the optimal operating temperature for performance and longevity.

This assembly is a direct replacement for several OEM and aftermarket part numbers, including Mercury 14586A3, Sierra 18-3549, GLM 13120, and Mallory 9-43014/9-43052.

• Engine Mount Installation
• Maintains engine operating temperature at 120°F / 50°C
• Complete kit includes thermostat and all required gaskets

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 120° Thermostat (14586)
• 1 x Gasket (27-19205002)
• 1 x Gasket (27-14318)
• 1 x Gasket (27-62386)

Installation Guide

1. Disconnect Battery: Ensure the engine is off and disconnect the negative battery cable for safety.
2. Locate Housing: Find the thermostat housing on the engine block, typically near the top of the cylinder head.
3. Drain Coolant: Place a container below the housing and carefully drain a sufficient amount of coolant.
4. Remove Cover: Loosen and remove the bolts securing the thermostat housing cover. Note their positions if they are different lengths.
5. Remove Old Parts: Take out the old thermostat and scrape away any existing gasket material from both the housing and the cover.
6. Clean Surfaces: Thoroughly clean the mating surfaces to ensure a perfect seal with the new gaskets.
7. Install New Parts: Insert the new thermostat, making sure it is oriented correctly. Place the new gaskets as required.
8. Reattach Cover: Secure the housing cover and tighten the bolts evenly in a crisscross pattern to the manufacturer's specified torque.
9. Refill Coolant: Top off the cooling system with the appropriate coolant.
10. Check for Leaks: Reconnect the battery, start the engine, and let it warm up. Carefully check for any leaks around the thermostat housing.

Troubleshooting & FAQ

Q: How do I confirm this fits my engine?

A: Check the "Compatible Engine Models" table, matching your engine's brand, model, HP, and year. For Mercury/Mariner engines, it is crucial to also verify your serial number against the ranges listed in the notes to ensure correct fitment.

Q: What is the difference between the 120°F and 122°F temperature ratings?

A: Our thermostat is rated for 120°F, which is the standard for the OEM Mercury part. Some aftermarket sources list 122°F, but this kit is designed to maintain the engine at the original specified operating temperature for optimal performance.

Q: When should I replace my thermostat?

A: Thermostats should be inspected annually and replaced if they are stuck open, closed, or show signs of heavy corrosion. Common signs of a failing thermostat include engine overheating (if stuck closed) or taking too long to reach proper operating temperature (if stuck open).

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.