140° Thermostat Kit – Fits MerCruiser V6/V8 Engines 4.3–8.2L (Replaces 807252Q4, 18-3668)

140° Thermostat Kit – Fits MerCruiser V6/V8 Engines 4.3–8.2L

This thermostat kit is designed for 1983–1996 MerCruiser GM V6 & V8 engines (4.3L to 8.2L) that use a standard cooling system and require a 140°F thermostat. It ensures your engine operates at the correct temperature for optimal performance and longevity.

This kit serves as a direct replacement for MerCruiser part numbers 807252Q4 and 807252T4, along with several other aftermarket equivalents.

• Includes a 140°F (60°C) thermostat and a complete set of housing gaskets for a full replacement.
• Compatible with a wide range of MerCruiser GM V6 and V8 engines from 262 to 502 CID.
• Engineered to meet or exceed original equipment specifications for fit and function.

Part Number Cross-Reference

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

Brand	Part Number
MerCruiser	807252Q4 / 807252T4
Sierra	18-3668
GLM	13390
Quicksilver	75-03948
Barr	59137

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

Specification	Value
Product Type	Engine Thermostat Kit
Thermostat Rating	140°F (60°C)
Application	Standard cooling systems
Compatibility	1983-1996 MerCruiser V6 & V8 GM engines
Housing Material	Brass sleeve (when included)
Dimensions	54mm diameter thermostat
Operating Temperature	140°F (60°C) opening temperature
Warranty	90 days (aftermarket)

Package Contents

• 1 x Thermostat (Replaces 807252T1, 59137)
• 1 x O-Ring (Replaces 25-30224)
• 1 x Gasket (Replaces 27-33179-2)
• 1 x Gasket (Replaces 27-47510)
• 1 x Gasket (Replaces 27-41812)

Note: This aftermarket kit does not include the brass sleeve (part #23-47508T). Please verify if your application requires this component before ordering.

Installation Guide

Professional installation is recommended. The following are general steps for reference:

1. Ensure the engine is completely cool and disconnect the battery. Drain the engine coolant into a suitable container.
2. Locate the thermostat housing on the engine. It is typically where the large coolant hose from the circulation pump connects to the intake manifold.
3. Carefully remove the bolts securing the thermostat housing cover. You may need to gently tap the housing to break the seal.
4. Remove the old thermostat and gasket. Note the orientation of the old thermostat for correct placement of the new one.
5. Thoroughly clean both the housing and cover mating surfaces to remove any old gasket material or corrosion.
6. Install the new 140° thermostat. Ensure it is seated correctly, typically with the jiggle pin or bleed hole in the uppermost position.
7. Place the new gasket onto the housing, aligning it with the bolt holes.
8. Reinstall the housing cover and tighten the bolts to the manufacturer's specified torque in a crisscross pattern.
9. Reconnect the coolant hose and refill the cooling system with the appropriate coolant mixture.
10. Reconnect the battery, start the engine, and let it warm up. Carefully check for any leaks around the thermostat housing.
11. Monitor the engine temperature gauge to ensure it maintains the correct operating temperature around 140°F.

Troubleshooting & FAQ

Q: How do I confirm this kit fits my MerCruiser engine?
A: Verify your engine model, year, and serial number against the detailed compatibility table on this page. It is crucial that your engine requires a 140°F thermostat for a standard cooling system, as specified for the models listed.

Q: What are the symptoms of a bad or failing thermostat?
A: Common signs include engine overheating, the engine temperature gauge reading unusually low, or large, erratic fluctuations in temperature. A stuck-open thermostat prevents the engine from reaching operating temperature, while a stuck-closed one will cause overheating.

Q: How often should I replace my engine's thermostat?
A: As a preventative maintenance item, it is recommended to inspect your thermostat annually and consider replacing it every 2-3 years, or immediately if you notice any cooling performance issues.

Q: Does this kit include the brass sleeve?
A: No, this specific kit does not include the brass sleeve (part #23-47508T). Some original housings require this sleeve for the thermostat to seat correctly. Please verify if your housing has or needs one before purchasing.

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.