Thermostat Housing Kit – Fits Mercury/Mariner Verado 135-400 HP (Replaces 892864T04, 8M0174561)

Thermostat Housing Kit – Fits Mercury/Mariner Verado 135-400 HP

This thermostat housing kit is a direct-fit replacement for Mercury and Mariner Verado four-stroke outboard engines from 135 HP to 400 HP (2004–present). It is engineered to ensure your engine maintains its optimal operating temperature by precisely regulating coolant flow for peak performance and longevity.

This assembly directly replaces Mercury part numbers 892864T04 and 8M0174561, along with Sierra aftermarket parts 18-3631 and 18-3631-K.

• Includes a pre-seated thermostat for simplified installation.
• Designed as a direct OEM-spec replacement for a perfect fit.
• Comes with the required O-ring seal for a leak-free installation.

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 with Housing Assembly (Replaces 892864T04/8M0174561)
• 1 x O-Ring Seal (Replaces 8M005958)
• 1 x Clamp (Note: Included with some kits, but may require separate purchase)

Installation Guide

1. Ensure the engine is completely cool and disconnect the battery.
2. Drain the engine coolant into a suitable container by opening the drain plug.
3. Locate the thermostat housing and carefully disconnect the attached coolant hoses.
4. Unbolt and remove the old thermostat housing assembly. Note the orientation.
5. Thoroughly clean the mounting surface on the engine block, removing all old gasket or sealant material.
6. Place the new O-ring seal into its groove on the new housing.
7. Install the new thermostat housing assembly, ensuring it is correctly seated.
8. Tighten the mounting bolts to the manufacturer's recommended torque specification.
9. Reconnect the coolant hoses and secure them with the clamps.
10. Close the drain plug and refill the cooling system with the appropriate coolant mixture.
11. Reconnect the battery, start the engine, and let it run for several minutes while checking for any leaks around the housing or hoses.

Troubleshooting & FAQ

Q: How do I confirm this thermostat kit fits my engine?
A: This kit fits a wide range of Mercury Verado L4 and L6 engines from 135 to 400 HP. The best way to confirm is to check your engine's model and serial number against the ranges listed in our "Compatible Engine Models" table above. Cross-referencing your old part number is also a reliable method.

Q: What is the difference between this aftermarket housing and the OEM version?
A: Original Mercury (OEM) housings are typically made from a composite material. Our aftermarket version is constructed from a durable metal alloy for enhanced longevity while maintaining the exact OEM specifications for fit and function.

Q: What are common signs that my thermostat housing is failing?
A: The most common symptoms include the engine overheating (running too hot) or taking too long to reach its normal operating temperature (running too cold). You may also notice visible coolant leaks from cracks in the old housing.

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.