120°F Thermostat Kit for Mercury/Mariner 6–25 HP 2-Stroke Outboards – Replaces Mercury 14586A3, Sierra 18-43052 and GLM 13121
120°F Thermostat Kit for Mercury/Mariner 6–25 HP 2-Stroke Outboards – Replaces Mercury 14586A3, Sierra 18-43052 and GLM 13121 is backordered and will ship as soon as it is back in stock.
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120°F Thermostat Kit for Mercury/Mariner 6–25 HP 2-Stroke Outboards...
120°F Thermostat Kit for Mercury/Mariner 6–25 HP 2-Stroke Outboards – Replaces Mercury 14586A3, Sierra 18-43052 and GLM 13121 is backordered and will ship as soon as it is back in stock.
Product Details
This aftermarket 120°F thermostat kit is designed for selected Mercury and Mariner 2-stroke outboard engines in the 6–25 HP range. It helps the engine reach and maintain its intended operating temperature for dependable cooling-system performance.
The kit is listed as a replacement for Mercury OEM reference 14586A3, Sierra 18-43052 and GLM 13121. These references identify the thermostat-kit application; always verify the engine model, stroke, serial number and gasket shape before installation.
- 120°F thermostat for compatible Mercury/Mariner applications.
- Designed for installation in the engine thermostat housing.
- Includes one thermostat and three application-specific gaskets.
- Use only the gasket that matches the engine housing; the remaining gaskets are not installed together.
Part Number Matrix
The following are manufacturer or aftermarket catalog references associated with this thermostat-kit application.
| Brand | Part Number | Reference Type |
|---|---|---|
| Mercury | 14586A3 | OEM replacement reference |
| Sierra | 18-43052 | Aftermarket thermostat-kit reference |
| GLM | 13121 | Aftermarket thermostat-kit reference |
Engine & Model Compatibility
This kit is cataloged for Mercury and Mariner 2-stroke outboards from 6 through 25 HP. Model, production year, country of manufacture and serial-number breakpoints can vary, so confirm the complete identification label on your engine before ordering.
| Brand | Application | Rated HP | Stroke | Reference | Fitment Note |
|---|---|---|---|---|---|
| Mercury/Mariner | Compact and small outboard applications | 6, 8, 9.9, 15 | 2-Stroke | 14586A3 | Verify the engine serial-number range and thermostat-housing gasket. |
| Mercury/Mariner | Small twin-cylinder outboard applications | 20, 25 | 2-Stroke | 14586A3 | Verify the engine serial-number range and thermostat-housing gasket. |
| Mercury/Mariner | Other listed applications within the catalog range | 6–25 | 2-Stroke | 18-43052 / 13121 | Do not use this listing for 4-stroke engines or applications outside the stated range. |
Fitment reminder: Horsepower alone is not sufficient to confirm compatibility. Compare the old thermostat, housing and gasket outline, and check the engine serial number against the applicable service information.
Technical Specifications
- Product Type
- Thermostat kit
- Thermostat Rating
- 120°F
- Application
- Mercury/Mariner 2-stroke outboards, 6–25 HP
- Installation Location
- Engine thermostat housing
- Connection
- Direct replacement application; verify fitment before installation
- Product Classification
- Aftermarket replacement, not an OEM-branded component
What’s in the Box
- 1 × 120°F thermostat
- 1 × gasket corresponding to OEM reference 27-62386
- 1 × gasket corresponding to OEM reference 27-14318-3
- 1 × gasket corresponding to OEM reference 27-19205-1
The cataloged kit contains multiple gasket options for different compatible housings. Install only the gasket that matches your engine; do not stack or combine the supplied gaskets.
Installation Notes
- Allow the engine to cool completely before servicing the thermostat housing.
- Disconnect the battery if required by the engine service procedure and keep the work area clear of fuel and ignition sources.
- Locate the thermostat housing and place a suitable drain pan beneath the work area.
- Remove the housing cover carefully, keeping track of bolt locations and inspecting the cover for damage.
- Remove the old thermostat and gasket. Note the thermostat orientation before removal.
- Clean the housing and cover mating surfaces completely without gouging them.
- Compare the supplied gaskets with the old gasket and housing, then install the correct gasket and thermostat in the proper orientation.
- Reinstall the housing cover and tighten the fasteners according to the engine manufacturer’s service-manual procedure.
- Run the engine using the appropriate water supply or test tank and check for leaks and proper cooling-water discharge.
Use the applicable Mercury or Mariner service manual for torque values, thermostat orientation and engine-specific testing procedures.
Troubleshooting & FAQ
How do I know if the thermostat may be failing?
Possible symptoms include overheating, running below normal operating temperature, irregular temperature behavior or reduced engine performance. A restricted cooling passage, water-pump problem or sensor issue can cause similar symptoms, so diagnose the complete cooling system.
Why are three gaskets included?
The kit is intended for multiple compatible Mercury/Mariner housings. The gasket shapes correspond to different applications. Select the single gasket that matches your housing and original part.
Does this fit a 4-stroke outboard?
No fitment is stated here for 4-stroke engines. This listing is for the cataloged 6–25 HP 2-stroke applications. Confirm the stroke type and serial number before purchase.
Can I install it myself?
Installation may be straightforward for an experienced marine technician, but incorrect thermostat orientation, gasket selection or fastener tightening can cause leaks or cooling problems. Follow the engine service manual or use a qualified technician.
Is this an OEM part?
This is an aftermarket replacement kit. Mercury, Mariner, Sierra and GLM names and part numbers are used only to identify compatible reference applications.
How should I confirm fitment?
Match the engine brand, model, horsepower, 2-stroke configuration and serial number. Also compare the thermostat housing and gasket profile with the supplied parts before installation.
Safety & Important Information
- Work only on a fully cooled engine and follow the manufacturer’s marine-service safety procedures.
- Do not operate the outboard without an adequate cooling-water supply.
- Verify the thermostat, housing and gasket shape against the original parts before installation.
- Do not use this listing as confirmation for engines outside the stated 6–25 HP, 2-stroke Mercury/Mariner application range.
- This is an aftermarket replacement, not an OEM component.
About Sea Sierra
- Marine replacement parts selected for practical service and repair applications.
- Clear reference-number and fitment information to help support accurate part selection.
- Customer support for installation and compatibility questions.
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