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

Product Details

This 140° Thermostat Kit – Fits MerCruiser V6/V8 Engines 4.3–8.2L (Replaces 807252Q4, 18-3668) is designed for MerCruiser GM V6 and V8 engines (4.3L, 5.0L, 5.7L, 7.4L, 8.2L) manufactured between 1983 and 1996 that utilize a 140° thermostat in a standard cooling system. It ensures your engine maintains the correct operating temperature for optimal performance and longevity.

It serves as a direct replacement for MerCruiser 807252Q4/807252T4, Sierra 18-3668, GLM 13390, Quicksilver 75-03948, and Barr 59137.

• Engineered for standard (raw water) cooling systems.
• Opens at a consistent 140°F (60°C) to regulate engine temperature.
• Includes multiple gaskets to fit a wide range of V6 and V8 applications.

Part Number Matrix

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

Engine & Model Compatibility

Confirm your engine model and year in the table below. For MerCruiser engines, verifying your serial number against the ranges provided in the 'Notes' column is crucial for ensuring a correct fit.

Technical Specs

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)

What’s in the Box

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

Note: Some aftermarket kits include a brass sleeve (23-47508T), while others do not. This specific kit's inclusions are as listed above.

Installation Notes

1. Disconnect the boat's battery before beginning work.
2. Drain the engine coolant to a level below the thermostat housing.
3. Carefully remove the bolts securing the thermostat housing cover.
4. Note the orientation of the old thermostat before removing it from the housing.
5. Thoroughly clean the mating surfaces of the housing and engine block to ensure a good seal.
6. Install the new thermostat in the correct orientation, followed by the appropriate new gasket from the kit.
7. Re-secure the housing cover and tighten the bolts to the manufacturer's specified torque.
8. Refill the cooling system with the recommended coolant.
9. Reconnect the battery, start the engine, and carefully check for any leaks as it warms up.
10. Ensure the engine reaches its normal operating temperature, confirming the thermostat opens correctly.

Troubleshooting & FAQ

Safety & Important Info

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

About Sea Sierra

• Pro-Grade Standards — We supply marine parts engineered to OEM-level tolerances and tested for real-world conditions.
• Fast Global Fulfillment — Free standard delivery to most regions, typically arriving in 5–15 days.
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