140°F Thermostat Kit – Fits MerCruiser V6/V8 4.3-8.2L (Replaces 807252Q4)

140°F Thermostat Kit – Fits MerCruiser V6/V8 4.3-8.2L (Replaces 807252Q4)

This thermostat kit is designed for a wide range of Mercury MerCruiser V6 and V8 gasoline stern drive engines (262-454 CID) manufactured from 1983 to 2016. It is engineered for models with standard cooling systems that specify a 140°F thermostat and does not fit high-performance engines.

This kit is a direct replacement for the following OEM and aftermarket part numbers: Mercury/MerCruiser 807252Q4, 807252T4, 807252T7, 8M0089715; Sierra 18-3668; GLM 13390; and Mallory 9-43150.

• Engineered for MerCruiser V6 & V8 models with standard cooling systems.
• Maintains a consistent engine operating temperature of 140°F (60°C).
• Includes a complete set of gaskets and O-rings for a comprehensive 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 (8M6002714)
• 1 x O-Ring (25-30224)
• 1 x Gasket Thermostat Housing Cover (27-33179-2)
• 1 x Gasket Thermostat Cover (27-41812)
• 1 x Gasket Thermostat Housing (27-47510)
• 1 x Gasket Lower Housing (27-530451/27-48818-1)
• 1 x Gasket (27-33918)

Installation Guide

1. Ensure the engine is completely cool. Drain the engine coolant into a suitable container by opening the drain plugs.
2. Locate the thermostat housing, which is typically on the top front of the engine where the main coolant hose connects.
3. Remove the bolts securing the housing cover. You may need to gently tap the housing to break the seal.
4. Note the orientation of the old thermostat before removing it from the housing.
5. Remove the old thermostat and any gasket or O-ring remnants from both the housing and the engine block.
6. Thoroughly clean the mating surfaces to ensure a clean, dry, and smooth surface for the new gaskets.
7. Install the new thermostat in the correct orientation. Place the new gaskets and O-rings as required by your specific engine model.
8. Reinstall the thermostat housing cover and tighten the bolts to the manufacturer's specified torque.
9. Reinstall all drain plugs and refill the cooling system with the appropriate coolant mixture.
10. Start the engine and allow it to reach operating temperature, checking for any leaks around the housing. Top off coolant as needed after the system purges any air.

Troubleshooting & FAQ

How do I confirm this thermostat kit fits my engine?
This kit is designed for MerCruiser V6 and V8 engines (1983-2016) with standard cooling systems. It is crucial to check your engine's model and serial number against the "Compatible Engine Models" table above. This kit is not for high-performance models.

What are the symptoms of a bad thermostat?
Common signs of a failing thermostat include the engine overheating (if stuck closed) or running too cold/taking too long to warm up (if stuck open). Poor engine performance, increased fuel consumption, and erratic temperature gauge readings can also indicate a problem.

Why is a 140°F thermostat used?
This 140°F thermostat is specified for raw water cooled engines to help prevent salt and mineral buildup that can occur at higher temperatures. Using the correct temperature-rated thermostat is essential for engine longevity and performance.

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.