Thermostat (160°F/71°C) – Fits MerCruiser 3.0-7.4L V6/V8 (Replaces 8072522, 807252T2, 8M0109441)

Thermostat (160°F/71°C) – Fits MerCruiser 3.0-7.4L V6/V8

This Sierra 18-3649 marine thermostat is engineered for MerCruiser 3.0L to 7.4L GM EFI and carbureted engines. It is compatible with both Alpha and Bravo sterndrive models from 1987 and newer that require a 160°F (71°C) thermostat for fresh water (closed) cooling systems.

This component is a direct replacement for a wide range of part numbers, ensuring broad compatibility for various engine setups. It is designed to meet or exceed original equipment specifications for reliable engine temperature regulation.

• Operating Temperature: 160°F (71°C)
• Cooling System Compatibility: Fresh Water Cooling Systems Only
• Installation Type: Internal, Engine Cooling System

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.

Confirm your engine model/year in the table below.

Technical Specifications

Package Contents

• 1 x Thermostat (8M0109441)

Installation Guide

1. Ensure the engine is completely cool before starting.
2. Drain the engine coolant into a suitable container.
3. Locate the thermostat housing, typically at the front top of the engine where the main coolant hose connects.
4. Remove the bolts securing the thermostat housing. Note their placement for reassembly.
5. Carefully lift the housing and remove the old thermostat. Note its orientation.
6. Clean both the housing and engine mounting surfaces, removing any old gasket material or sealant residue.
7. Install the new thermostat in the correct orientation.
8. Place the new gasket onto the housing or engine block as required.
9. Re-secure the thermostat housing and tighten the bolts to the manufacturer's recommended torque.
10. Refill the cooling system with the appropriate coolant mixture.
11. Start the engine and let it run, checking carefully for any leaks around the thermostat housing.
12. Once the engine reaches operating temperature, re-check the coolant level and top off if necessary.

Troubleshooting & FAQ

How do I confirm this thermostat fits my engine?
First, check the "Compatible Engine Models" table on this page. This thermostat is designed specifically for MerCruiser 3.0L to 7.4L models from 1987 and newer with fresh water cooling systems. Cross-reference your existing part number with our list to ensure an exact match.

What temperature does this thermostat operate at?
This is a 160°F (71°C) thermostat. It is critical to use the correct temperature-rated thermostat specified for your engine to ensure optimal performance and prevent overheating or running too cool.

What are the signs of a failing marine thermostat?
Common symptoms include engine overheating, the engine not reaching its normal operating temperature, erratic temperature gauge readings, or visible coolant leaks from the thermostat housing area.

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.