Thermostat Kit – Fits Mercury/Mariner 70-125 HP 2-Stroke (Replaces 803061T1)
Thermostat Kit – Fits Mercury/Mariner 70-125 HP 2-Stroke (Replaces 803061T1) 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 Kit – Fits Mercury/Mariner 70-125 HP 2-Stroke (Replaces ...
Thermostat Kit – Fits Mercury/Mariner 70-125 HP 2-Stroke (Replaces 803061T1) is backordered and will ship as soon as it is back in stock.
Product Details
This Thermostat Kit – Fits Mercury/Mariner 70-125 HP 2-Stroke (Replaces 803061T1) provides a reliable, direct-fit replacement for maintaining the cooling system on inline 3 & 4 cylinder outboards from 1987 and newer. Engineered to regulate engine temperature, this kit ensures your motor operates within its optimal temperature range, preventing both overheating and overcooling.
This component is a direct interchange for Sierra 18-3569, Sierra 18-3549/18-0339, GLM 13124, Mallory 9-43155/9-43014/9-60004, and GHmarine 18-3569.
- Engineered as a direct OEM-equivalent replacement.
- Essential for routine cooling system maintenance and repair.
- Includes thermostat, seal, gasket, and washer for a complete installation.
Part Number Matrix
Use this matrix to confirm equivalent references across OEM and aftermarket.
| Brand | Part Number |
|---|---|
| Sierra | 18-3569 |
| Sierra | 18-3549/18-0339 |
| GLM | 13124 |
| Mallory | 9-43155/9-43014/9-60004 |
| GHmarine | 18-3569 |
| Mercury | 803061T1 |
Engine & Model Compatibility
Confirm your engine model/year in the table below.
Fits Mercury/Mariner 2-stroke inline 3 & 4 cylinder outboards from 1987 and newer.
| Brand | Model | Rated HP | Stroke | Years | OEM Part No. | Notes |
|---|---|---|---|---|---|---|
| Mercury | 70 | 70 | 2-Stroke | 1987+ (A996142 & UP) | 803061T1 | 3 Cylinder |
| Mercury | 75 | 75 | 2-Stroke | 1990+ (C222000 & UP) | 803061T1 | 3 Cylinder |
| Mercury | 80 | 80 | 2-Stroke | 1987–1990 (A996142 & UP) | 803061T1 | 3 Cylinder |
| Mercury | 90 | 90 | 2-Stroke | 1987–2007+ (A996142 & UP) | 803061T1 | 3 Cylinder |
| Mercury | 100 | 100 | 2-Stroke | 1987+ (B209468 & UP) | 803061T1 | 4 Cylinder |
| Mercury | 115 | 115 | 2-Stroke | 1987+ (C100000 & UP) | 803061T1 | 4 Cylinder |
| Mercury | 125 | 125 | 2-Stroke | 1987+ (D283222 & UP) | 803061T1 | 4 Cylinder |
Technical Specs
- Product Type
- Thermostat Kit
- Installation
- Direct OEM replacement
- Temperature Rating
- 122°F / 50°C (primary); some sources indicate 120°F
- Housing Material
- Brass/Copper (thermostat), Metal (housing components)
- Housing Color
- Copper/Brass with Black/Gray Gaskets
- Operating Temperature
- 122°F / 50°C (opening temperature)
- Warranty
- 1 Year (aftermarket versions)
- Other Technical Attributes
- For cooling system maintenance
What’s in the Box
- 1 x Thermostat (14586)
- 1 x Thermostat Seal (62386001)
- 1 x Thermostat Cover Gasket (430068)
- 1 x Washer (47533)
Installation Notes
- Ensure the engine is off and cool. Disconnect the battery.
- Locate the thermostat housing on the engine block.
- Place a drain pan below the housing and remove the drain plug, if equipped, to drain coolant from the powerhead.
- Loosen and remove the bolts securing the thermostat cover.
- Carefully remove the cover, old gasket, and the old thermostat. Note the orientation of the thermostat.
- Clean the mating surfaces of the housing and cover, removing all old gasket material.
- Install the new thermostat in the correct orientation, followed by the new seal and gasket.
- Reinstall the cover and tighten the bolts to the manufacturer's specified torque.
- Refill the cooling system. Reconnect the battery.
- Start the engine and check for leaks and proper operating temperature.
Troubleshooting & FAQ
How do I know if this thermostat kit fits my engine?
First, check the compatibility table and match your engine's brand, model, horsepower, and year or serial number range. It is critical to also visually compare the parts in the photos to your existing thermostat and housing to ensure a perfect match before ordering.
What are the signs of a failing outboard thermostat?
A thermostat can fail stuck open or stuck closed. A stuck-open thermostat will cause the engine to run too cool, leading to poor performance and fuel economy. A stuck-closed thermostat will cause the engine to overheat, which can result in serious damage. An alarm horn or fluctuating temperature gauge are key indicators.
When should I replace my thermostat?
It's good practice to replace the thermostat as part of routine cooling system maintenance, especially every few years in saltwater environments. You should replace it immediately if you notice any signs of engine overheating or incorrect operating temperature.
What temperature does this thermostat open at?
This thermostat is rated to begin opening at approximately 122°F (50°C). Minor variations in temperature ratings (e.g., 120°F) exist across different aftermarket sources, but performance is functionally identical.
Is this a complete kit for the job?
This kit includes the thermostat, thermostat seal, cover gasket, and washer, which are the essential components for a standard replacement. You may need additional tools and sealant depending on your engine's condition.
Why do some kits for the same part number show different contents?
While the core thermostat is the same, some aftermarket manufacturers may bundle slightly different gaskets or hardware. The components listed in "What's in the Box" are exactly what you will receive with this kit.
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.
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