143°F Marine Outboard Thermostat – Fits Mercury Mariner 135–200 HP EFI and Select Johnson/Evinrude Models
143°F Marine Outboard Thermostat – Fits Mercury Mariner 135–200 HP EFI and Select Johnson/Evinrude Models 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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143°F Marine Outboard Thermostat – Fits Mercury Mariner 135–200 HP ...
143°F Marine Outboard Thermostat – Fits Mercury Mariner 135–200 HP EFI and Select Johnson/Evinrude Models is backordered and will ship as soon as it is back in stock.
Product Details
This replacement 143°F (62°C) marine thermostat is a single thermostat for selected Mercury/Mariner and Johnson/Evinrude outboard applications. The company fitment data identifies Mercury/Mariner 135–200 HP EFI applications and additional Johnson/Evinrude applications including 40–250 HP E-TEC, 6–55 HP, crossflow V4 and V6 models, and 9.9 HP and 15 HP four-stroke models from 1994–2001.
For Mercury/Mariner applications, the company records also list selected models and serial ranges from 7.5 HP through V300/3.4L, including 7.5 HP serial 5226935 and up, 9.8 HP serial 5206550 and up, 40 HP serial 3336258–C159199, 50/60 HP serial D000750 and up, 65 HP serial 3547987–4571651, 70 HP serial 4571652–4825248, 70/75/80/90 HP serial A996142 and up, 100/115 HP serial B209468 and up, V135/V150 serial A904646 and up, V175 serial C100861 and up, V200 serial 6435503 and up, V220 serial B117316 and up, V225 serial 5628028 and up, V300/3.4L serial 5611648 and up, and XR4 and Magnum II serial C239553–D081999. Confirm your exact model, serial number, and thermostat reference before ordering.
- Single aftermarket thermostat for selected marine outboard cooling systems.
- 143°F (62°C) operating temperature rating.
- Designed as a direct replacement when the listed reference and fitment conditions match.
- Aftermarket replacement; not an OEM-branded component.
Part Number Matrix
Use the following references to compare your existing thermostat. A reference-number match should be confirmed against the complete engine model and serial-number conditions.
| Brand or source | Reference numbers |
|---|---|
| Mercury/Mariner | 62981 / 66850 / 75692 / 75692B2 / 75692Q2 / 75692T |
| Johnson/Evinrude/OMC | 377148 / 378065 / 393659 / 434841 / 437414 / 5005440 / 508626 |
| Sierra | 18-3543 / 18-3553 |
| GLM | 13010 |
| Other listed aftermarket reference | 9-43019 / 9-43101 |
Engine & Model Compatibility
Compatibility is application-specific. Keep horsepower, engine family, stroke type, model, and serial-number conditions together when checking fitment.
| Brand | Application | Rated HP | Stroke or engine type | Year or serial condition | Reference |
|---|---|---|---|---|---|
| Mercury/Mariner | EFI outboard applications | 135–200 | Verify engine type | Verify model and serial number | 62981, 66850, 75692 family |
| Mercury/Mariner | Selected small and mid-range applications | 7.5–115 | Verify engine type | Specific serial ranges listed by the manufacturer; confirm before purchase | 75692 family |
| Mercury/Mariner | V135, V150, V175, V200, V220, V225, V300/3.4L | 135–300 | V-engine applications | Specific model and serial ranges listed by the manufacturer; confirm before purchase | 75692 family / Sierra 18-3553 |
| Johnson/Evinrude | E-TEC applications | 40–250 | 2-stroke E-TEC | Verify model and year | 393659, 434841, 378065, 508626, 5005440 |
| Johnson/Evinrude | Various outboard applications | 6–55 | 2-stroke | Verify model and year | Listed Johnson/Evinrude references |
| Johnson/Evinrude | 9.9 HP and 15 HP applications | 9.9 / 15 | 4-stroke | 1994–2001 | Listed Johnson/Evinrude references |
| Johnson/Evinrude | Crossflow V4 and V6 applications | Verify engine rating | 2-stroke V4/V6 | Verify model and year | Listed Johnson/Evinrude references |
Technical Specs
- Product Type
- Marine outboard thermostat
- Temperature Rating
- 143°F (62°C)
- Product Configuration
- Single thermostat; not a seals or gasket kit
- Installation
- Direct replacement when the reference number and complete fitment conditions match
- Brand Status
- Aftermarket replacement, not OEM-branded
What’s in the Box
- 1 x 143°F (62°C) thermostat
Gaskets, seals, carriers, poppets, washers, and other service parts are not included unless specifically stated in the package contents.
Installation Notes
- Switch off the engine, allow it to cool completely, and follow the service manual’s safety procedure.
- Confirm the thermostat reference, engine model, horsepower, stroke type, and serial number before removing the original part.
- Locate the thermostat housing and place a suitable drain pan beneath the work area if water may drain during service.
- Remove the housing cover and note the orientation of the original thermostat.
- Clean the mating surfaces carefully and remove old gasket material without damaging the housing.
- Install the replacement thermostat in the correct orientation. Use a new gasket or seal if required by the engine service manual; none is included with this single thermostat.
- Reinstall the housing cover and tighten fasteners evenly to the manufacturer’s specified torque.
- Run the engine according to the service manual and check for water leakage and proper cooling-system operation.
Troubleshooting & FAQ
How do I know if an outboard thermostat may be failing?
Possible symptoms include overheating, an engine that runs unusually cool, poor temperature stability, restricted cooling-water flow, or a thermostat that is visibly corroded or stuck open or closed. Diagnose the complete cooling system before replacing the thermostat.
Why is the 143°F rating important?
The thermostat controls the engine’s operating temperature within the range specified for the application. Use the temperature rating required by your exact engine; do not substitute a different rating solely because the part looks similar.
Can this thermostat be used in saltwater?
It is intended for the listed marine outboard applications. Saltwater use increases corrosion risk, so follow the engine manufacturer’s flushing and cooling-system maintenance recommendations.
Is a new gasket required?
A new gasket or seal is commonly recommended when servicing a thermostat housing, but this listing contains the thermostat only. Select the gasket specified for your exact engine separately if required.
Is this an OEM thermostat?
No. This is an aftermarket replacement intended to match the listed manufacturer references and fitment conditions. Mercury, Mariner, Johnson, Evinrude, OMC, Sierra, and GLM references are used for identification and cross-reference purposes only.
How should I verify fitment?
Compare the complete reference number and thermostat temperature rating, then verify the engine brand, model, horsepower, stroke or engine type, year where applicable, and serial-number range. If any of these details differ, consult the engine service manual before ordering.
Shipping speed and cost
Available shipping methods, delivery estimates, and shipping charges are shown at checkout and may vary by destination.
Warranty and returns
Warranty coverage and return eligibility are governed by the current store policies. Contact customer support with your order details if the part arrives damaged or appears to be incorrect.
Safety & Important Info
- Verify the complete application and reference number before purchase; horsepower alone does not confirm compatibility.
- Do not rely on a general model range when the engine has a specific serial-number condition.
- Allow the engine to cool before opening the thermostat housing.
- Use the manufacturer’s service manual for torque values, gasket requirements, orientation, and cooling-system testing.
- This is an aftermarket replacement, not an OEM component.
- Professional installation is recommended when the correct procedure or fitment is uncertain.
About Sea Sierra
- Marine Replacement Parts — We supply aftermarket marine components selected for listed applications and service needs.
- Application-Focused Listings — Confirm model, reference, and serial conditions before ordering.
- Customer Support — Contact us with your engine details and existing part reference when you need help checking fitment.
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