18-3668 807252Q04 Thermostat Kit 140 Degree for Mercruiser 4.3 5.0 5.7 7.4 8.2L | JLM Marine

Thermostat Kit 140 Degree for Mercruiser 4.3L 5.0L 5.7L 7.4L 8.2L Engines

This 140°F (60°C) thermostat kit is designed for Mercruiser stern drive engines, including popular 4.3L, 5.0L, 5.7L, 7.4L, and 8.2L models. It provides reliable temperature regulation to maintain optimal engine performance and prevent overheating in demanding marine conditions.

This aftermarket kit directly replaces Mercruiser 807252Q4, 807252T4, 807252T7, 8M0089715, Sierra 18-3668, and GLM 13390. It includes all necessary gaskets, O-rings, and the thermostat element for a complete installation.

• Complete Kit: Includes thermostat, cover gaskets, housing gasket, and O-ring
• 140°F Operating Temperature: Ensures proper engine cooling across various operating conditions
• Direct Replacement: Fits standard Mercruiser thermostat housings without modification

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.

Technical Specifications

Package Contents

This complete thermostat kit includes all components necessary for installation:

• 18-2552 Thermostat Cover Gasket (replaces 27-33179-2)
• 18-2553 Thermostat Cover Gasket (replaces 27-47510)
• 18-2554 Thermostat Cover Gasket (replaces 27-41812)
• 18-3551 Thermostat 140°F (replaces 59137)
• 18-7173 O-Ring (replaces 25-30224)
• 18-2917 Thermostat Housing Gasket (replaces 27-53045-1, 27-3391)

Note: Multiple gaskets are included to ensure compatibility with various Mercruiser thermostat housing configurations.

Installation Guide

1. Allow the engine to cool completely and ensure the ignition is off before beginning work.
2. Drain the cooling system to below the thermostat housing level to minimize coolant loss.
3. Locate the thermostat housing on your engine block and remove the mounting bolts securing the cover.
4. Carefully lift the thermostat cover and remove the old thermostat and gasket. Clean all mating surfaces thoroughly to remove old gasket material and debris.
5. Select the correct gasket(s) from the kit that match your thermostat housing configuration.
6. Install the new thermostat into the housing with the spring side facing toward the engine block.
7. Position the new gasket(s) and O-ring onto the housing, ensuring proper alignment with all bolt holes.
8. Reinstall the thermostat cover and tighten mounting bolts in a cross-pattern to the manufacturer's specified torque.
9. Refill the cooling system with the appropriate coolant mixture and bleed air from the system per manufacturer instructions.
10. Start the engine and check for leaks around the thermostat housing. Monitor engine temperature to confirm proper thermostat operation.

Troubleshooting & FAQ

Q: How do I confirm this thermostat kit fits my Mercruiser engine?
A: Check your engine displacement (4.3L, 5.0L, 5.7L, 7.4L, or 8.2L) and compare your current thermostat part number against the cross-reference table above. If your original part matches any listed number, this kit is compatible.

Q: Which gasket should I use from the kit?
A: The kit includes multiple gaskets to fit different Mercruiser housing configurations. Compare each gasket to your old one and use the gasket(s) that match your housing's shape and bolt pattern. Some housings may require more than one gasket.

Q: How often should I replace my thermostat?
A: Most marine thermostats should be replaced every 2–3 years or whenever you notice symptoms like overheating, poor cabin heat, or temperature fluctuations. Regular replacement prevents corrosion buildup and ensures reliable temperature control.

Q: What are the signs that my thermostat is failing?
A: Common symptoms include engine running too hot or too cold, erratic temperature gauge readings, and poor heater performance. A stuck-closed thermostat causes overheating, while a stuck-open thermostat prevents the engine from reaching normal operating temperature.

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.