140°F Thermostat Kit – Fits MerCruiser V6/V8 4.3-8.2L (Replaces Mercury/MerCruiser 807252Q4, 807252T4, 807252T7, 8M0089715)
140°F Thermostat Kit – Fits MerCruiser V6/V8 4.3-8.2L (Replaces Mercury/MerCruiser 807252Q4, 807252T4, 807252T7, 8M0089715) is backordered and will ship as soon as it is back in stock.
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Delivery and Shipping
Delivery and Shipping
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140°F Thermostat Kit – Fits MerCruiser V6/V8 4.3-8.2L (Replaces Mer...
140°F Thermostat Kit – Fits MerCruiser V6/V8 4.3-8.2L (Replaces Mercury/MerCruiser 807252Q4, 807252T4, 807252T7, 8M0089715) is backordered and will ship as soon as it is back in stock.
Product Details
This 140°F Thermostat Kit – Fits MerCruiser V6/V8 4.3-8.2L (Replaces 807252Q4) is engineered for Mercury MerCruiser V6 and V8 gasoline stern drive engines (262-454 CID) manufactured from 1983 to 2016. It is designed for standard cooling systems and does not fit high-performance models.
This kit provides a direct replacement for multiple OEM and aftermarket part numbers, including Mercury/MerCruiser 807252Q4, Sierra 18-3668, and GLM 13390.
- Designed for standard cooling systems on specified MerCruiser engines.
- Maintains a consistent 140°F (60°C) engine operating temperature.
- Includes the thermostat and all required gaskets for a complete installation.
Part Number Matrix
Use this matrix to confirm equivalent references across OEM and aftermarket.
| Brand | Part Number |
|---|---|
| Mercury/MerCruiser | 807252Q4 |
| Mercury/MerCruiser | 807252T4 |
| Mercury/MerCruiser | 807252T7 |
| Mercury/MerCruiser | 8M0089715 |
| Sierra | 18-3668 |
| GLM | 13390 |
| Mallory | 9-43150 |
Engine & Model Compatibility
Confirm your engine model/year in the table below.
For MerCruiser engines, please verify your model and serial number range to ensure correct fitment. This thermostat is not compatible with high-performance models.
| 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
- Temperature Rating
- 140°F (60°C)
- Installation
- Standard Cooling System
- Application
- MerCruiser V6 & V8 Engines (except high performance models)
- Housing Material
- Metal/Brass
- Weight
- 0.08 kg (0.18 lbs)
- Warranty
- 1-Year (Aftermarket)
What’s in the Box
- 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 Notes
- Disconnect the battery and allow the engine to cool completely before starting work.
- Place a suitable container below the engine to catch draining coolant, then drain the cooling system.
- Locate and remove the bolts securing the thermostat housing, then remove the housing itself.
- Take out the old thermostat and all associated gaskets. Thoroughly clean the mating surfaces to remove any debris or old gasket material.
- Install the new thermostat, ensuring it is correctly oriented as per your engine's service manual. Place the new gaskets in their proper positions.
- Reinstall the thermostat housing cover and tighten the bolts to the manufacturer-specified torque. Do not overtighten.
- Refill the cooling system with the correct type and amount of coolant.
- Reconnect the battery, start the engine, and carefully check for any leaks around the housing as the engine comes up to temperature.
Troubleshooting & FAQ
How do I know if this thermostat kit fits my engine?
Confirm your exact model, year, and horsepower from the "Engine & Model Compatibility" table. It is critical to also cross-reference the serial number ranges listed in the 'Notes' column to ensure a perfect match, as fitment can vary within the same model year.
What are the signs of a failing thermostat?
Common symptoms include the engine overheating, running too cold (temperature gauge stays low), erratic temperature readings, or coolant leaks appearing around the thermostat housing. A stuck-open thermostat typically causes the engine to warm up very slowly, while a stuck-closed thermostat will lead to rapid overheating.
Why use a 140°F thermostat instead of a hotter one?
The 140°F temperature rating is specifically for raw (sea, lake, or river) water-cooled marine engines. This lower operating temperature helps prevent salt, mineral, and sediment deposits from building up inside the engine's cooling passages. Using a higher-rated thermostat in a raw-water system can lead to blockages and overheating. Always use the temperature rating specified by your engine's manufacturer.
Is this kit compatible with high-performance engines?
No. This thermostat kit is designed exclusively for standard-duty MerCruiser V6 and V8 engines. High-performance and racing engines have different cooling system demands and often require different thermostat designs and temperature ratings.
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.
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 in 5–15 days.
- Manufacturer-Direct Value — Fair pricing without compromising on materials or QC.
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