SKU: 25835684760

Thermostat Kit – Fits Mercury/Mariner 70-125 HP 2-Stroke (Replaces 803061T1)

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Description

Thermostat Kit – Fits Mercury/Mariner 70-125 HP 2-Stroke (Replaces 803061T1)Thermostat Kit Fits Mercury Mariner 70 125 HP 2 Stroke (Replaces 803061T1) This thermostat kit is designed for Mercury Mariner 70 125 HP 2 stroke inline 3 & 4 cylinder outboards from 1987 and newer. It ensures your engine maintains the correct operating temperature for optimal performance and longevity. This kit serves as a direct replacement for several OEM and aftermarket part numbers, offering a reliable and cost effective solution for your cooling

Thermostat Kit – Fits Mercury/Mariner 70-125 HP 2-Stroke (Replaces 803061T1)

This thermostat kit is designed for Mercury/Mariner 70-125 HP 2-stroke inline 3 & 4 cylinder outboards from 1987 and newer. It ensures your engine maintains the correct operating temperature for optimal performance and longevity.

This kit serves as a direct replacement for several OEM and aftermarket part numbers, offering a reliable and cost-effective solution for your cooling system maintenance.

  • Includes all necessary gaskets and seals for a complete installation.
  • Engineered to meet or exceed OEM specifications for fit and function.
  • Rated to open at 122°F / 50°C to regulate engine temperature.

Part Number Cross-Reference

Use this table to confirm equivalent part numbers across OEM and aftermarket brands.

Brand Part Number
Mercury (OEM) 803061T1
Sierra 18-3569
Sierra 18-3549 / 18-0339
GLM 13124
Mallory 9-43155 / 9-43014 / 9-60004
GHmarine 18-3569

Compatible Engine Models

Confirm your engine model/year in the table below. For Mercury owners, here’s a guide to help you identify your engine’s serial/model: Mercury Serial Number Guide. You can also review exploded diagrams to verify part numbers: Mercury Parts Diagrams & Catalog.

80
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 802-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 Specifications

Specification Value
Product Type Thermostat Kit
Installation Direct OEM replacement
Temperature Rating 122°F / 50°C (Note: some sources may list 120°F)
Housing Material Brass/Copper (thermostat), Metal (housing components)
Housing Color Copper/Brass with Black/Gray Gaskets
Fitting Type Direct fit to thermostat housing
Operating Temperature 122°F / 50°C (opening temperature)
Warranty 1 Year (aftermarket versions)
Other Technical Attributes For cooling system maintenance

Package Contents

  • 1 x Thermostat (14586)
  • 1 x Thermostat Seal (62386001)
  • 1 x Thermostat Cover Gasket (430068)
  • 1 x Washer (47533)

Installation Guide

Refer to your engine’s service manual for detailed instructions. The general steps for replacement are as follows:

  1. Safety First: Disconnect the battery cables and ensure the engine is cool to the touch.
  2. Drain Coolant: Place a container under the engine and carefully drain the cooling system.
  3. Access Housing: Locate and remove the bolts securing the thermostat housing cover.
  4. Remove Old Parts: Take out the old thermostat, gasket, and seal. Note their orientation.
  5. Clean Surfaces: Thoroughly clean the mating surfaces of the housing and cover, removing any old gasket material or corrosion.
  6. Install New Thermostat: Place the new thermostat into the housing, ensuring it is correctly oriented. Install the new gasket and seal.
  7. Reassemble: Re-install the housing cover and tighten the bolts to the manufacturer's specified torque.
  8. Refill System: Refill the cooling system with the recommended coolant.
  9. Check for Leaks: Reconnect the battery, start the engine, and let it reach operating temperature. Carefully check for any leaks around the housing.

Troubleshooting & FAQ

Q: How can I be sure this thermostat kit fits my specific Mercury outboard?
A: The best way is to match your engine's serial number to the ranges listed in the "Compatible Engine Models" table. You can find your serial number on the engine's transom bracket. Our Mercury Serial Number Guide can help you locate it.

Q: What are the signs of a faulty thermostat?
A: Common symptoms include the engine overheating at various speeds or, conversely, failing to reach its normal operating temperature. An inaccurate temperature gauge reading can also indicate a problem.

Q: What temperature does this thermostat operate at?
A: This thermostat is designed to open at 122°F (50°C). This allows the engine to warm up quickly and then regulates the temperature to prevent overheating.

Q: How often should I replace my outboard's thermostat?
A: It is recommended to replace the thermostat and gaskets as part of your regular cooling system service, typically every 1-2 years or 100-200 hours, especially if operating in saltwater. Always refer to your owner's manual for specific maintenance intervals.

Q: OEM vs. Aftermarket?
A: This listing is an aftermarket replacement part (not an OEM component). We build to OEM specifications using comparable-grade materials. Production is done in an ISO9002-certified facility, and each batch is inspected for consistent performance.

Q: How fast do you ship and how much does it cost?
A: We offer fast global shipping—typically 5–15 days worldwide—and standard shipping is free. Expedited options are available at checkout depending on your location.

Q: What is your warranty and return policy?
A: This product includes a 1-year warranty against manufacturing defects under normal use. If something goes wrong, contact our support team with your order details. Returns are accepted within our standard return window (unused & in original condition); please see our policy page or reach out for instructions.

Important Notes

  • Verify that the product images and specifications match your original part. If discrepancies exist—even if your model is listed—do not proceed with the purchase.
  • This product is an aftermarket replacement part and is not an OEM component.
  • Professional installation is recommended to ensure safety and optimal performance.

Why Choose JLM MARINE?

  • Quality Assured: As a trusted manufacturer for over 20 years, we supply top marine brands globally.
  • Fast Global Shipping: Free delivery worldwide in 5–15 days.
  • Direct from Manufacturer: Competitive pricing without compromising quality.
Shipping Notes
  • Free Standard Shipping on $100+ Orders to the USA.
  • Except Preorder products are shipped in 48 hours.
  • Delivery to the USA:
  1. Standard Shipping : 3-10 business days
  • If time is of the essence, please consider selecting expedited delivery for faster service.
Exchange/Return Notes
  • We offer a 30-day return/exchange service after receiving.
  • Final sale items are not eligible for returns or exchanges.
  • To process your return/exchange, please contact us at [email protected]
  • Please click here for more details>>> Return & Exchange Policy
SKU: 25835684760

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★★★★★ 4
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Very supportive for the big chested girlies! Material is comfortable and sweat wicking. I’d recommend sizing down for a snug fit.
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Reviewed in the United States on January 25, 2026
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Nina Nakai
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★★★★★ 5
Nice fabric, comfortable, easy maintenance
Special Size: 27.5" Full Length, Size: Large, Color: Taupe, Special Size: 27.5" Full Length, Size: Large, Color: Taupe
I ordered a medium and they’re actually a size large. And they are just too large. I should’ve gotten the small, as recommended I thought I was ordering medium and I think I would’ve been OK with a medium, but where I usually wear a small and they sent me a large. It was just ridiculously large. They are lightweight and they are warm. I’m a senior and I’m thin so I get cold very easily especially in early morning and evening, so I like to wear them in the morning for my walks/yoga , they also work nicely under a longish skirt so it’s not so sheer… will definitely get more but will go with the small size. Just for reference, I’m 5 foot seven I usually wear a small or a size 5/6 usa size so these were too large, particularly in the waist just overall they were too large, but I think even if I got a small size they’re still gonna be kind of large in the stomach. I have an hourglass shape just for reference, but they are very comfortable, and I love the fabric. I am keeping them because I like the fabric and I really need them. I just will not wear them out of the house right now because they’re not fitting properly but next go round we’ll get the right size. Price was right they were having a sale so it was a bit of an impulse buy. But hello it was only 10 bucks! so that’s why it’s not worth sending it back for me. Overall, very nice quality and would recommend. Cats like the fabric too! 😸
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Reviewed in the United States on May 4, 2026
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Angela Borchetta
Omaha, US
★★★★★ 5
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Special Size: 27.5" Full Length with Pockets, Size: Small, Color: Taupe
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Reviewed in the United States on May 17, 2026
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Denise L Notman
Lake Worth, US
★★★★★ 5
Not for people over 5'6"
Special Size: 27.5" Full Length with Pockets, Size: XX-Large, Color: Slate Grey
These are definitely designed for shorter people. They get 5* because they're still low cost and decent quality on fabric. Just have to pull the waist up because the calfs are not designed to be worn as capris and pull the entire leggings down. If it sized up one more then they'd just fall down because of the waist. So waistband fits as expected. They're just also for shorter people than me.
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★★★★★ 3
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