Thermostat Kit for MerCruiser Engines – Replaces 807252Q5 and 807252T8
Thermostat Kit for MerCruiser Engines – Replaces 807252Q5 and 807252T8 is backordered and will ship as soon as it is back in stock.
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Delivery and Shipping
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Thermostat Kit for MerCruiser Engines – Replaces 807252Q5 and 807252T8
Thermostat Kit for MerCruiser Engines – Replaces 807252Q5 and 807252T8 is backordered and will ship as soon as it is back in stock.
Product Details
This marine thermostat kit is an aftermarket replacement for selected MerCruiser cooling-system applications. It replaces MerCruiser/Mercury Marine part numbers 807252Q5 and 807252T8. The kit is identified in the Sierra catalog as thermostat kit 18-3647.
Use the original thermostat, gasket arrangement, engine model, and serial number to confirm fitment before ordering. Part-number interchange alone does not confirm compatibility with every MerCruiser engine or cooling-system configuration.
- Thermostat kit for selected MerCruiser marine engines.
- Supplied as a multi-piece service kit for thermostat replacement.
- Includes the thermostat and the listed housing and cover gaskets.
- Aftermarket replacement; not an original Mercury Marine component.
Part Number Matrix
These are the documented manufacturer and aftermarket references associated with this kit.
| Brand or Source | Part Number | Reference Type |
|---|---|---|
| MerCruiser / Mercury Marine | 807252Q5 | Replacement reference |
| MerCruiser / Mercury Marine | 807252T8 | Replacement reference |
| Sierra | 18-3647 | Thermostat kit reference |
Engine and Fitment Information
The available catalog evidence associates this kit with the MerCruiser/Mercury Marine replacement references listed above, but it does not establish one universal fitment range for all V6 and V8 engines. Confirm the exact engine model, serial number, cooling-system configuration, and thermostat arrangement against your service manual or the original part before installation.
| Brand | Application | Verification Required |
|---|---|---|
| MerCruiser / Mercury Marine | Selected inboard and sterndrive cooling-system applications using 807252Q5 or 807252T8 | Verify engine model, serial number, cooling system, and original thermostat kit |
Technical Specifications
- Product Type
- Thermostat kit
- Application
- Marine engine cooling system
- Installation
- Replacement installation
- Replacement References
- 807252Q5 and 807252T8
- Aftermarket Status
- Aftermarket replacement; not OEM
What’s in the Box
The catalog listing for this thermostat kit identifies the following components. Exact gasket form and quantity should be compared with the parts removed from the engine before installation.
- 1 x Thermostat
- 1 x Thermostat housing gasket
- 1 x Thermostat cover gasket
- 1 x Additional thermostat cover gasket
- 1 x Additional thermostat cover gasket
Catalog component references include thermostat reference 18-3551; housing gasket reference 18-2917; and cover gasket references 18-2844, 18-2553, and 18-2834. Gasket reference numbers are provided for identification and should not be treated as separate products included beyond the kit contents.
Installation Notes
- Allow the engine to cool completely before beginning work, and follow the safety procedures in the engine service manual.
- Disconnect the battery where required and close or isolate the appropriate water supply before removing the thermostat housing.
- Remove the thermostat housing or cover and note the orientation of the old thermostat and gasket arrangement.
- Clean the mating surfaces carefully, removing old gasket material without damaging the housing or engine surfaces.
- Compare the replacement thermostat and each supplied gasket with the original parts before assembly.
- Install the thermostat in the correct orientation and use the appropriate housing and cover gaskets supplied with the kit.
- Reassemble the housing using the manufacturer’s specified tightening sequence and torque values.
- Restore the cooling-system connections, start the engine according to the service manual, and check for leaks and proper temperature control.
Troubleshooting and FAQ
What part numbers does this kit replace?
This kit is documented as a replacement for MerCruiser/Mercury Marine part numbers 807252Q5 and 807252T8.
Is this a complete thermostat kit?
Yes. It is sold as a thermostat kit and includes the thermostat together with the listed housing and cover gaskets. Compare the supplied pieces with your original assembly before installation.
Does this kit fit every MerCruiser V6 or V8 engine?
No universal V6 or V8 fitment claim should be made from the replacement numbers alone. Verify the exact engine model, serial number, cooling-system configuration, and original thermostat references before ordering.
Is this an OEM Mercury Marine part?
No. This is an aftermarket replacement kit that references Mercury Marine part numbers for identification and compatibility checking.
Should I replace the gaskets when replacing the thermostat?
Replacing the associated housing and cover gaskets is recommended when the thermostat housing is opened. Use the gasket that matches the applicable housing and cover surfaces.
What should I do if the supplied gasket does not match?
Do not force the part into place or reuse an incorrect gasket. Stop installation and verify the engine model, serial number, cooling-system configuration, and original part numbers.
Safety and Important Information
- Verify the engine model, serial number, cooling-system configuration, and original part numbers before purchase.
- Compare the replacement thermostat and gasket shapes with the original parts before installation.
- Use the engine manufacturer’s service information for coolant or water-system procedures, torque specifications, and temperature checks.
- Professional installation is recommended when the correct procedure or fitment is uncertain.
About Sea Sierra
- Marine Replacement Parts — We supply aftermarket components for marine maintenance and repair applications.
- Fitment-Focused Listings — Product references are provided to help customers compare parts before ordering.
- Service Support — Always confirm the exact engine and original part configuration before installation.
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