Thermostat Kit – Fits Mercury/Mariner Verado 135-300HP (Replaces Mercury 892864T04, Sierra 18-3631)
Thermostat Kit – Fits Mercury/Mariner Verado 135-300HP (Replaces Mercury 892864T04, Sierra 18-3631) is backordered and will ship as soon as it is back in stock.
Worry-free returns
Worry-free returns
Shop with confidence. If you’re not completely satisfied, eligible items may be returned within the return window, provided they are unused and in original packaging.
If the return is due to our error or a defective item, we’ll make it right.
Please contact us before returning any item.
Delivery and Shipping
Delivery and Shipping
Orders are typically processed within 1–2 business days.
U.S. orders usually arrive within 6–15 days, depending on stock location and destination.
International delivery times may vary due to customs processing.
Tracking information will be provided once your order ships.
Thermostat Kit – Fits Mercury/Mariner Verado 135-300HP (Replaces Me...
Thermostat Kit – Fits Mercury/Mariner Verado 135-300HP (Replaces Mercury 892864T04, Sierra 18-3631) is backordered and will ship as soon as it is back in stock.
Product Details
This Thermostat Kit for Mercury Verado 135-300 HP is designed for Mercury and Mariner Verado four-stroke outboard engines from 135HP to 300HP (2005–present). It plays a crucial role in maintaining optimal engine operating temperature by precisely regulating coolant flow, ensuring efficient performance and preventing overheating.
It serves as a direct replacement for Mercury part numbers 892864T04 and 8M0174561, as well as Sierra 18-3631.
- Engineered for direct-fit installation.
- Maintains a nominal opening temperature of 144°F (62°C).
- Includes the essential O-ring seal and clamp for a complete replacement.
Part Number Matrix
Use this matrix to confirm equivalent references across OEM and aftermarket brands.
| Brand | Part Number |
|---|---|
| Mercury | 892864T04 |
| Mercury | 8M0174561 |
| Sierra | 18-3631 |
Engine & Model Compatibility
Confirm your engine model and year in the table below.
This kit fits select four-stroke outboards under the Mercury and Mariner brands.
| Brand | Model | Rated HP | Stroke | Years | OEM Part No. | Notes |
|---|---|---|---|---|---|---|
| Mercury | Verado 4-Cylinder | 135 | 4-Stroke | 2005–present | 892864T04 | Also listed as 8M0174561 |
| Mercury | Verado 4-Cylinder | 150 | 4-Stroke | 2005–present | 892864T04 | Also listed as 8M0174561 |
| Mercury | Verado 4-Cylinder | 175 | 4-Stroke | 2005–present | 892864T04 | Also listed as 8M0174561 |
| Mercury | Verado 4-Cylinder | 200 | 4-Stroke | 2005–present | 892864T04 | Also listed as 8M0174561 |
| Mercury | Verado 6-Cylinder | 200 | 4-Stroke | 2005–present | 892864T04 | Also listed as 8M0174561 |
| Mercury | Verado 6-Cylinder | 225 | 4-Stroke | 2005–present | 892864T04 | Also listed as 8M0174561 |
| Mercury | Verado 6-Cylinder | 250 | 4-Stroke | 2005–present | 892864T04 | Also listed as 8M0174561 |
| Mercury | Verado 6-Cylinder | 275 | 4-Stroke | 2005–present | 892864T04 | Also listed as 8M0174561 |
| Mercury | Verado 6-Cylinder | 300 | 4-Stroke | 2005–present | 892864T04 | Also listed as 8M0174561 |
Technical Specs
- Product Type
- Thermostat Kit with Housing
- Installation
- Direct Replacement
- Temperature Rating
- 144°F (62°C)
- Housing Material
- Aluminum
- Operating Temperature
- 144°F (62°C) nominal opening temperature
- Other Technical Attributes
- Includes O-ring seal and clamp
What’s in the Box
- 1 x Thermostat Assembly (replaces 892864T04)
- 1 x O-ring Seal (replaces 8M005958)
- 1 x Clamp (replaces 888988008)
Installation Notes
- Ensure the engine is off and cool, and disconnect the battery for safety.
- Drain the engine coolant to a level below the thermostat housing.
- Locate the thermostat housing. Remove any hoses and mounting bolts to access the old thermostat.
- Remove the old thermostat, housing, and O-ring. Clean both mating surfaces of any old gasket material or corrosion.
- Install the new thermostat and O-ring into the housing. Ensure the thermostat is oriented correctly.
- Mount the new housing assembly and tighten the bolts to the manufacturer's specified torque.
- Reconnect all hoses and secure with clamps.
- Refill the cooling system with the recommended coolant.
- Reconnect the battery, start the engine, and let it warm up. Check for any leaks and verify the engine reaches its normal operating temperature.
Troubleshooting & FAQ
How do I know if my thermostat is failing?
Common signs of a faulty thermostat include engine overheating alarms, the engine temperature gauge showing abnormally high or low readings, or erratic temperature fluctuations. A thermostat stuck open will prevent the engine from reaching its proper operating temperature, while one stuck closed will cause it to overheat quickly.
What is the operating temperature of this unit?
This thermostat is designed to begin opening at a nominal temperature of 144°F (62°C) to allow coolant to circulate through the engine block, effectively regulating its operating temperature.
Will this fit any Mercury Verado engine?
This kit is specifically designed for 4-cylinder and 6-cylinder Mercury Verado models from 135HP to 300HP manufactured from 2005 to the present. Always verify fitment by checking your OEM part number against the ones listed in our Part Number Matrix.
Is this a complete kit for the job?
Yes, this is a comprehensive kit that includes the thermostat, a new housing, the rubber O-ring seal, and the necessary clamp. This provides all the essential components for a standard thermostat replacement.
OEM vs. Aftermarket?
This listing is an aftermarket replacement (not OEM). It is built to OEM-level specifications with comparable materials. Manufactured in an ISO 9002 facility, it is batch-inspected for consistency and reliability.
Shipping speed & cost?
We ship worldwide quickly—typical transit is 5–15 days. Standard shipping is free; expedited options appear at checkout where available.
Warranty & returns?
This product is covered by a 1-year warranty against manufacturing defects under normal use. If any issues arise, contact our support team with your order details. Returns are accepted within our standard window, provided the item is unused and in its original condition. See our full policy page or reach out for instructions.
Safety & Important Info
- Verify images and specifications against your original part. If anything differs—even if your model appears compatible—do not purchase.
- This is an aftermarket replacement component, not an OEM part.
- 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 quality control.
Payment & Security
Payment methods
Your payment information is processed securely. We do not store credit card details nor have access to your credit card information.
