Thermostat Kit – Fits Mercury/Mariner 4-Stroke 8-40 HP Outboard Motors (Replaces 825212A1, 825212001, 855676003)

Thermostat Kit – Fits Mercury/Mariner 4-Stroke 8-40 HP Outboard Motors

This thermostat kit is designed for Mercury and Mariner 4-stroke outboard engines ranging from 8 to 40 horsepower, manufactured between 1995 and 2018. It includes compatibility with various specific models such as the 30 HP (1999–2005), 40 HP (1998–2018), and 50 HP (1995–2000) engines.

The kit directly replaces Mercury part numbers 825212A1, 825212001, 855676003, and more, ensuring a straightforward installation for maintaining engine temperature regulation.

• Package includes thermostat, ring rubber seal, and housing gasket
• Compatible with gasoline-powered engines
• Installation method: direct replacement

Part Number Cross-Reference

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

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.

Technical Specifications

Package Contents

• 1 x Thermostat (825212A1)
• 1 x Ring Rubber Seal
• 1 x Housing Gasket (27-824853)
• 1 x Installation Instructions

Installation Guide

1. Ensure the engine is cool and disconnect the battery to prevent accidental starting.
2. Remove the existing thermostat housing and carefully extract the old thermostat and gaskets.
3. Clean the mounting surfaces thoroughly to ensure proper sealing.
4. Install the new thermostat, ring rubber seal, and housing gasket included in the kit.
5. Reinstall the thermostat housing securely, ensuring no leaks.
6. Reconnect the battery and start the engine to check for proper operation and to verify there are no leaks.

Troubleshooting & FAQ

• How do I confirm this thermostat fits my engine? Check your engine's model and serial number against the compatible engine models table. For Mercury engines, use the Mercury Serial Number Guide linked above.
• How does this aftermarket thermostat differ from the OEM? This listing is an aftermarket replacement part (not an OEM component). It is built to OEM specifications using comparable-grade materials and produced in an ISO9002-certified facility with quality inspections.
• How often should I replace the thermostat? Replacement intervals vary by engine usage and conditions; commonly, it is recommended during routine maintenance or if overheating or cooling issues are detected.
• What are common signs of a failing thermostat? Symptoms include engine overheating, temperature fluctuations, or poor heating performance, which may indicate the thermostat is stuck open or closed.
• OEM vs. Aftermarket? 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.
• How fast do you ship and how much does it cost? 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.
• What is your warranty and return policy? 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.