Thermostat (130°F/54°C) – Fits Mercury/Mariner 200-300HP (Replaces 885599003, 885599004, 8M0057307)
Thermostat (130°F/54°C) – Fits Mercury/Mariner 200-300HP (Replaces 885599003, 885599004, 8M0057307) 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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Thermostat (130°F/54°C) – Fits Mercury/Mariner 200-300HP (Replaces ...
Thermostat (130°F/54°C) – Fits Mercury/Mariner 200-300HP (Replaces 885599003, 885599004, 8M0057307) is backordered and will ship as soon as it is back in stock.
Product Details
This is a replacement Thermostat (130°F/54°C) designed for a wide range of Mercury and Mariner 200-300 HP V6 engines, including EFI, DFI, Optimax, Pro XS, and XS models manufactured between 2002 and 2017. It ensures your engine maintains the correct operating temperature for optimal performance and fuel efficiency.
It serves as a direct replacement for Mercury OEM parts 885599003, 885599004, and 8M0057307, as well as aftermarket equivalents like Sierra 18-3535 and WSM 775-15.
- Installs as a direct OEM-equivalent replacement.
- Regulates engine temperature by opening at 130°F (54°C).
- Includes one thermostat per package.
Part Number Matrix
Use this matrix to confirm equivalent references across OEM and aftermarket.
| Brand | Part Number |
|---|---|
| Mercury | 885599003 |
| Mercury | 885599004 |
| Mercury | 8M0057307 |
| Sierra | 18-3535 |
| WSM | 775-15 |
Engine & Model Compatibility
Confirm your engine model/year in the table below.
This thermostat is designed for various 6-cylinder Mercury and Mariner outboards from 200 HP to 300 HP.
| Brand | Model | Rated HP | Stroke | Years | OEM Part No. | Notes |
|---|---|---|---|---|---|---|
| Mercury | 6 Cyl 3.625 Bore 3.0L EFI | 225 | 4-Stroke | 2002–2003 | 885599003, 885599004, 8M0057307 | |
| Mercury | 6 Cyl 3.625 Bore 3.0L EFI | 250 | 4-Stroke | 2006–2008 | 885599003, 885599004, 8M0057307 | |
| Mercury | 6 Cyl 3.625 Bore 3.0L XB | 250 | 4-Stroke | 2002–2003 | 885599003, 885599004, 8M0057307 | |
| Mercury | 6 Cyl 3.6265 Bore 3.2L XS | 300 | 4-Stroke | 2006–2017 | 885599003, 885599004, 8M0057307 | |
| Mercury | 6 Cyl 3.6265 Bore 3.0L Optimax | 200 | 2-Stroke | 2003–2006 | 885599003, 885599004, 8M0057307 | |
| Mercury | 6 Cyl 3.6265 Bore 3.0L Optimax | 250 | 2-Stroke | 2009–2014 | 885599003, 885599004, 8M0057307 | |
| Mercury | 6 Cyl 3.6265 Bore 3.0L Pro XS | 225 | 2-Stroke | 2004–2010 | 885599003, 885599004, 8M0057307 | |
| Mercury | 200 DFI 3.0L | 200 | 2-Stroke | 885599003, 885599004, 8M0057307 | (serial OG386496-Up) | |
| Mercury | 225 HP 3.0L Carb & EFI | 225 | 4-Stroke | 885599003, 885599004, 8M0057307 | (serial OD280813-Up) | |
| Mercury | 225 DFI | 225 | 2-Stroke | 885599003, 885599004, 8M0057307 | (serial OG129222-Up) | |
| Mercury | 250 3.0L EFI | 250 | 4-Stroke | 885599003, 885599004, 8M0057307 | (serial OG1219222-Up) | |
| Mercury | 225XS / Sport XS / Pro XS | 225 | 2-Stroke | 885599003, 885599004, 8M0057307 | ||
| Mercury | 250XS / Sport XS / Pro XS | 250 | 2-Stroke | 885599003, 885599004, 8M0057307 | ||
| Mercury | 300X | 300 | 885599003, 885599004, 8M0057307 | |||
| Mercury | 300XS | 300 | 885599003, 885599004, 8M0057307 |
Technical Specs
- Product Type
- Engine Thermostat
- Installation
- Direct OEM Replacement
- Temperature Rating
- 130°F (54°C)
- Operating Temperature
- 130°F (54°C) open temperature
- Warranty
- Manufacturer dependent (typically 1 year)
What’s in the Box
- 1 x Thermostat (885599003/885599004/8M0057307)
Installation Notes
- Disconnect the battery before beginning work.
- Allow the engine to cool completely.
- Drain the engine coolant into a suitable container.
- Locate the thermostat housing on the engine and remove the cover.
- Remove the old thermostat and any gasket material.
- Clean the housing and cover surfaces thoroughly.
- Install the new thermostat, ensuring it is correctly oriented. Use a new gasket if required.
- Reinstall the thermostat housing cover and tighten bolts to the manufacturer's recommended torque.
- Refill the cooling system with the appropriate coolant.
- Reconnect the battery, start the engine, and check for any leaks as it warms up.
Troubleshooting & FAQ
How do I know if my thermostat is failing?
Common signs of a faulty thermostat include engine overheating, temperature gauge reading irregularly (too high or too low), and poor engine performance. If the thermostat is stuck open, the engine may not reach its optimal operating temperature. If stuck closed, it will overheat.
Is a gasket included with this thermostat?
This listing is for the thermostat only. Gaskets are sold separately. It is highly recommended to replace the gasket during thermostat installation to ensure a proper seal.
Can I use a different temperature thermostat?
It is critical to use the thermostat with the OEM-specified temperature rating for your engine. Using a thermostat with a different temperature can lead to improper engine performance, increased emissions, and potential engine damage.
How often should a marine thermostat be replaced?
While there is no fixed interval, it is good practice to inspect the thermostat during routine cooling system service (e.g., every 2-3 years or 200-300 hours) and replace it if there are signs of corrosion or if it fails a function test.
OEM vs. Aftermarket?
This listing is an aftermarket replacement (not OEM). Built to OEM-level specifications with comparable materials. Manufactured in an ISO 9002 facility, batch-inspected for consistency.
Shipping speed & cost?
We ship worldwide quickly—typical transit 5–15 days. Standard shipping is free; expedited options appear at checkout where available.
Warranty & returns?
Covered by a 1-year warranty against manufacturing defects under normal use. If issues arise, contact support with your order details. Returns are accepted within our standard window (unused & in original condition). See our policy page or reach out for instructions.
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.
Payment & Security
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