140° Thermostat Kit – Fits MerCruiser V6 & V8 Engines (Replaces 807252Q4)

$39.99 $63.00

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140° Thermostat Kit – Fits MerCruiser V6 & V8 Engines (Replaces 807252Q4) is backordered and will ship as soon as it is back in stock.

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Product Details

This 140° Thermostat Kit – Fits MerCruiser V6 & V8 Engines is engineered for General Motors-manufactured MerCruiser V6 and V8 engines (262-454 CID) from 1983 to 2016. It is designed for models with standard cooling systems that require a 140°F thermostat and does not fit high-performance variants.

It serves as a direct replacement for multiple OEM and aftermarket part numbers, including Mercury/Quicksilver 807252Q4, Sierra 18-3668, and GLM 13390.

Operates at a 140°F (60°C) opening temperature.
Designed for standard cooling systems in specified MerCruiser engines.
Includes thermostat, O-ring, and all necessary housing gaskets for a complete installation.

Part Number Matrix

Use this matrix to confirm equivalent references across OEM and aftermarket.

Brand	Part Number
Mercury/Quicksilver	807252Q4
Mercury/Quicksilver	807252T4
Mercury/Quicksilver	807252T7
Mercury/Quicksilver	8M0089715
Sierra	18-3668
GLM	13390
Mallory	9-43150

Engine & Model Compatibility

Confirm your engine model/year in the table below.

This kit fits a wide range of MerCruiser V6 and V8 engines manufactured by General Motors between 1983–2016. Verify your model and serial number range below to ensure correct fitment.

Brand	Model	Rated HP	Stroke	Years	OEM Part No.	Notes
MerCruiser	4.3L V6 175/185/205	175-205	4-Stroke	1985–1987	807252Q4	Model years 0A331455-0B775129
MerCruiser	4.3L V6	175-205	4-Stroke	1987–1995	807252Q4	Model years 0B773243-0F601126
MerCruiser	4.3L/LX GM	175-205	4-Stroke	1993–1995	807252Q4	Model years 0F000878-0F601126
MerCruiser	5.0L & 5.7L Small Block	200-260	4-Stroke	1983–1984	807252Q4	Model years 6218462-6899057
MerCruiser	5.0L	200-230	4-Stroke	1988–1995	807252Q4	Model years 0B774445-0F600999
MerCruiser	5.0LX	230	4-Stroke	1988–1995	807252Q4	Model years 5907058-0F600999
MerCruiser	5.7L/5.7MIE/SKI	260-350	4-Stroke	1988–1995	807252Q4	Model years 0B773305-0F600999
MerCruiser	5.7L Ski	260-350	4-Stroke	1985–1995	807252Q4	Model years 0A338533-0F775199
MerCruiser	7.4L/MIE	330-340	4-Stroke	1988–1994	807252Q4	Model years 0B771113-0F351999
MerCruiser	8.2L MIE	380+	4-Stroke	1990–1992	807252Q4	Model years 0C878221-0D857199

Technical Specs

Product Type: Thermostat Kit
Installation: Standard Cooling System
Temperature Rating: 140°F (60°C)
Operating Temperature: 140°F (60°C) nominal opening
Housing Material: Brass Sleeve
Dimensions: 16.5" H x 8.5" W x 8.5" L
Weight: 0.25 lb (0.11 kg)
Warranty: 1-year (aftermarket)
Fitment Note: For standard cooling systems only; not for use with high-performance engines

What’s in the Box

1 x Thermostat (8M6002714/59137)
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) (Note: Inclusion may vary by kit)

Installation Notes

Ensure the engine is completely cool and disconnect the battery for safety.
Drain the engine coolant or raw water to a level below the thermostat housing.
Locate and carefully remove the bolts securing the thermostat housing. Note the position of any brackets or hoses.
Remove the old thermostat and gasket/seal from the housing or manifold and discard them.
Thoroughly clean the mating surfaces of the housing and manifold, removing all old gasket material or corrosion.
Install the new thermostat in the correct orientation, followed by the new gasket or seal as required.
Reinstall the thermostat housing cover and tighten the bolts to the manufacturer's recommended torque specifications.
Refill the cooling system. Start the engine and let it warm up, checking carefully for any leaks around the housing. Top off coolant if necessary.

Troubleshooting & FAQ

How do I confirm this thermostat kit fits my engine?

This kit is for GM-based MerCruiser V6 and V8 engines (1983–2016) with standard cooling systems. To ensure compatibility, compare your engine model and year to the "Engine & Model Compatibility" table on this page. Do not use this kit for high-performance models.

What are the signs of a failing engine thermostat?

Common symptoms include engine overheating, running too cold (not reaching proper operating temperature), erratic temperature gauge readings, and potential coolant leaks from the thermostat housing area.

What's the difference between a 140°F and a 160°F thermostat?

The temperature rating indicates when the thermostat opens. A 140°F thermostat is typically used in raw/saltwater-cooled engines to reduce salt and mineral buildup. A 160°F or higher thermostat is common in freshwater/closed-cooling systems for better fuel efficiency. Always use the temperature specified by your engine's manufacturer.

Is it necessary to replace all the included gaskets?

Yes. To prevent leaks and ensure a proper seal, you should always replace all old gaskets and O-rings with the new ones provided in the kit whenever you change the thermostat.

How often should a marine thermostat be replaced?

As a preventative measure, it's good practice to inspect your thermostat annually and replace it every 2-3 years, especially in saltwater environments. Replace it immediately if you notice any signs of cooling system problems.

OEM vs. Aftermarket?

This listing is an aftermarket replacement (not OEM). Built to OEM-level specifications with comparable materials. Manufactured in an ISO 9002 facility, batch-inspected for consistency.

Shipping speed & cost

We ship worldwide quickly—typical transit 5–15 days. Standard shipping is free; expedited options appear at checkout where available.

Warranty & returns

Covered by a 1-year warranty against manufacturing defects under normal use. If issues arise, contact support with your order details. Returns are accepted within our standard window (unused & in original condition). See our policy page or reach out for instructions.

Safety & Important Info

Verify images/specifications vs your original part. If anything differs—even if your model appears compatible—do not purchase.
This is an aftermarket replacement, not an OEM component.
Professional installation is recommended for safety and performance.

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