Thermostat Kit – Fits Mercury/Mariner 70–125 HP 2-Stroke (Replaces 803061T1, 803061T02)
Thermostat Kit – Fits Mercury/Mariner 70–125 HP 2-Stroke (Replaces 803061T1, 803061T02) is backordered and will ship as soon as it is back in stock.
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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.
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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, 803061T02) 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) is designed for a range of Mercury and Mariner outboards from 1987 and newer. It is compatible with 3-cylinder models (70, 75, 80, 90 HP) and 4-cylinder models (100, 115, 125 HP), ensuring reliable engine temperature regulation for optimal performance.
This kit serves as a direct interchange for Sierra 18-3569, GLM 13124, Mallory 9-43155, and Mercury 803061T1/803061T02.
- Engineered for direct OEM-replacement installation.
- Complete kit includes the thermostat, gasket, and seal.
- Maintains a consistent operating temperature of 50°C (120°F).
Part Number Matrix
Use this matrix to confirm equivalent references across OEM and aftermarket.
| Brand | Part Number |
|---|---|
| Sierra | 18-3569 |
| GLM | 13124 |
| Mallory | 9-43155 |
| Mercury | 803061T1 / 803061T02 |
Engine & Model Compatibility
Confirm your engine model/year in the table below.
This thermostat kit is designed for a range of Mercury and Mariner 3-cylinder and 4-cylinder 2-stroke outboards from 1987 and newer.
| Brand | Model | Rated HP | Stroke | Years | OEM Part No. | Notes |
|---|---|---|---|---|---|---|
| Mercury | 3-cyl | 70 | 2-Stroke | 1987 and newer | 803061T1 | A996142 & UP |
| Mercury | 3-cyl | 75 | 2-Stroke | 1987 and newer | 803061T1 | C222000 & UP |
| Mercury | 3-cyl | 80 | 2-Stroke | 1987 and newer | 803061T1 | A996142 & UP |
| Mercury | 3-cyl | 85 | 2-Stroke | 1987 and newer | 803061T1 | |
| Mercury | 3-cyl | 90 | 2-Stroke | 1987 and newer | 803061T1 | A996142 & UP |
| Mercury | 4-cyl | 100 | 2-Stroke | 1987 and newer | 803061T1 | B209468 & UP |
| Mercury | 4-cyl | 115 | 2-Stroke | 1987 and newer | 803061T1 | C100000 & UP |
| Mercury | 4-cyl | 125 | 2-Stroke | 1987 and newer | 803061T1 | D283222 & UP |
Technical Specs
- Product Type
- Thermostat Kit
- Installation
- Direct OEM Replacement
- Fuel Type
- Gasoline
- Operating Temperature
- 50°C / 120°F
- Weight
- 0.1 kg (0.22 lbs)
- Warranty
- Limited Lifetime (Sierra)
- Included Components
- Complete kit includes thermostat, gasket and seal
What’s in the Box
- 1 x Thermostat (18-3549)
- 1 x Thermostat Gasket (18-0182)
- 1 x Thermostat Cover Gasket (18-0339)
Installation Notes
- Ensure the engine is off and cool. Disconnect the battery for safety.
- Drain the engine block coolant into a suitable container.
- Locate and unbolt the thermostat housing cover.
- Carefully remove the old thermostat and discard the old gaskets/seals.
- Thoroughly clean the mating surfaces of the housing and cover, removing any old gasket material or corrosion.
- Install the new thermostat, ensuring it is oriented correctly.
- Place the new gaskets and seals in their correct positions.
- Re-install the housing cover and tighten the bolts to the manufacturer's specified torque.
- Refill the cooling system with the recommended coolant.
- Reconnect the battery, start the engine, and check for any leaks around the housing as the engine warms up.
Troubleshooting & FAQ
How do I know if my thermostat has failed?
Common signs of a faulty thermostat include the engine overheating at idle or low speeds, or taking an unusually long time to reach its proper operating temperature. You might also receive temperature alarms from your gauges.
What is the correct operating temperature for this thermostat?
This thermostat is designed to open at 50°C (120°F), helping the engine maintain a stable temperature for efficient operation.
Will this fit my specific engine serial number?
This kit fits a wide range of Mercury/Mariner engines from 1987 and newer. To ensure a perfect match, please compare your engine's serial number against the ranges listed in the compatibility table (e.g., "A996142 & UP").
What's the difference between this kit and the OEM part?
This aftermarket kit is manufactured to meet or exceed original equipment (OEM) specifications for fit, form, and function. It provides a cost-effective solution and includes all necessary gaskets for a complete installation.
How often should I replace my outboard's thermostat?
For preventative maintenance, it's good practice to inspect the thermostat annually and consider replacement every 2-3 years, especially when operating in saltwater environments. Replace it immediately if you notice signs of failure.
Is this an OEM part or an aftermarket replacement?
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 quality.
What are the shipping speed and cost?
We ship worldwide quickly—typical transit time is 5–15 days. Standard shipping is free for most orders; expedited options will appear at checkout if available for your location.
What is the warranty and return policy?
This product is covered by a 1-year warranty against manufacturing defects under normal use. If you encounter any issues, please contact our support team with your order details. Returns are accepted within our standard window for items that are unused and in their original condition. See our policy page or reach out for instructions.
Safety & Important Info
- Verify images and specifications against your original part before purchasing. If anything differs—even if your model appears compatible—do not purchase.
- This is an aftermarket replacement part, not an original equipment manufacturer (OEM) component.
- Professional installation is highly recommended for safety and optimal performance.
About Sea Sierra
- Pro-Grade Standards — We supply marine parts engineered to OEM-level tolerances and rigorously tested for real-world conditions.
- Fast Global Fulfillment — We offer free standard delivery to most regions, with an average transit time of 5–15 days.
- Manufacturer-Direct Value — By working directly with manufacturers, we provide fair pricing without compromising on materials or quality control.
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