140°F Thermostat Kit for MerCruiser V8 Engines — Replaces Mercury Marine 807252Q3 / 807252T6
140°F Thermostat Kit for MerCruiser V8 Engines — Replaces Mercury Marine 807252Q3 / 807252T6 is backordered and will ship as soon as it is back in stock.
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Delivery and Shipping
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140°F Thermostat Kit for MerCruiser V8 Engines — Replaces Mercury M...
140°F Thermostat Kit for MerCruiser V8 Engines — Replaces Mercury Marine 807252Q3 / 807252T6 is backordered and will ship as soon as it is back in stock.
Product Details
This 140°F Thermostat Kit is an aftermarket replacement kit for selected MerCruiser V8 marine engines, including Chevy V8 and Ford V8 applications listed for this thermostat family. It is intended to help restore the specified operating temperature and proper thermostat-housing sealing during cooling-system service.
The kit is listed as a replacement for Mercury Marine OEM references 807252Q3 and 807252T6. Sierra catalog cross-reference information identifies the corresponding aftermarket thermostat kit as 18-3646.
- 140°F (approximately 60°C) thermostat rating.
- Designed for selected MerCruiser V8 applications.
- Includes the thermostat and multiple application-specific housing and cover gaskets.
- Aftermarket replacement; verify the thermostat, housing, gasket configuration and engine application before ordering.
Part Number Matrix
These references are provided for identification and cross-reference purposes. Confirm the application and gasket configuration against your engine before installation.
| Brand or Source | Part Number | Reference Type |
|---|---|---|
| Mercury Marine | 807252Q3 | OEM reference |
| Mercury Marine | 807252T6 | OEM replacement reference |
| Sierra | 18-3646 | Aftermarket kit cross-reference |
Engine & Model Compatibility
The available catalog evidence identifies this 140°F thermostat kit for selected MerCruiser V8 engines. Exact fitment can vary by engine design, thermostat housing and gasket arrangement, so use the OEM reference and compare the removed parts before installation.
| Engine Brand | Engine Family | Configuration | Thermostat Rating | OEM Reference | Fitment Notes |
|---|---|---|---|---|---|
| MerCruiser | Chevy V8 | 4-stroke marine inboard or sterndrive application | 140°F | 807252Q3 | Selected applications; verify housing and gasket arrangement. |
| MerCruiser | Ford V8 | 4-stroke marine inboard or sterndrive application | 140°F | 807252Q3 | Selected applications; verify housing and gasket arrangement. |
Technical Specs
- Product Type
- Thermostat kit
- Thermostat Rating
- 140°F (approximately 60°C)
- Application
- Selected MerCruiser V8 marine engines
- Replacement Type
- Aftermarket replacement for specified OEM references
- Included Sealing Parts
- Thermostat housing and cover gaskets for the listed application family
- Installation
- Direct replacement when the engine, housing and gasket arrangement match
What’s in the Box
- 1 x 140°F thermostat
- 1 x thermostat housing gasket
- 3 x thermostat cover gaskets in different application configurations
Use only the gasket that matches the original housing and cover. The remaining gasket options are not necessarily used on every engine.
Installation Notes
- Disconnect the battery and allow the engine to cool completely before beginning service.
- Close the seacock or otherwise isolate the water supply as applicable to the vessel and cooling-system design.
- Drain or remove enough water or coolant to prevent spillage when the thermostat housing is opened.
- Remove the thermostat housing and note the original thermostat orientation and gasket arrangement.
- Clean the housing and mating surfaces without gouging or damaging them.
- Install the new thermostat in the same orientation as the original part.
- Select and install the single housing or cover gasket that matches the original configuration. Do not stack unused gasket options.
- Reinstall the housing and tighten fasteners to the engine manufacturer’s specified torque.
- Restore the cooling-system water or coolant supply according to the engine and vessel service instructions.
- Run the engine, bring it to operating temperature and check for leaks and abnormal temperature behavior.
Troubleshooting & FAQ
Is this a 140°F or 160°F thermostat?
This kit is specified as a 140°F (approximately 60°C) thermostat kit. Do not substitute a 160°F thermostat unless it is specifically required by the exact engine application.
Which engines does this kit fit?
Catalog references identify the replacement for selected MerCruiser V8 applications, including Chevy V8 and Ford V8 engine families. Exact fitment depends on the engine and thermostat-housing configuration. Confirm the OEM reference, thermostat rating and gasket arrangement before purchase.
Why are several gaskets included?
Different MerCruiser thermostat housings and covers use different gasket shapes. The kit provides several gasket options, but only the gasket that matches your specific housing should be installed.
Does the kit include a thermostat sleeve or brass sleeve?
No separate brass or thermostat sleeve is listed for this 140°F replacement kit. A sleeve should not be assumed to be included unless it is specifically shown with the supplied contents.
What are common signs of a failing thermostat?
Possible symptoms include overheating, running below the expected operating temperature, unstable temperature readings or leakage around the thermostat housing. Other cooling-system faults can produce similar symptoms, so inspect the complete system before replacing parts.
Can I use every gasket in the package?
No. The gasket options are supplied for different housing configurations. Install only the one that matches the original gasket and mating surfaces.
Is this an OEM part?
This listing is for an aftermarket replacement kit. The OEM references are provided to help confirm application and cross-reference the replacement.
Safety & Important Information
- Verify the OEM reference, thermostat rating, housing shape and gasket pattern before ordering.
- Do not rely on engine horsepower or year alone to determine fitment.
- Allow the engine to cool before opening any cooling-system component.
- Follow the engine manufacturer’s service instructions for torque, sealing, water supply and coolant procedures.
- Professional installation is recommended when the cooling-system configuration or fitment is uncertain.
About Sea Sierra
- Marine replacement parts selected for practical service and repair applications.
- Application-focused product information to help match parts before installation.
- Customer support for product questions and order assistance.
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