MerCruiser Thermostat Kit – 807252T4
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The Mercury MerCruiser Thermostat Kit 807252T4 is a genuine OEM thermostat service kit designed for GM-based V6 and V8 MerCruiser engines using closed cooling (freshwater cooling) systems. This kit is calibrated for higher operating temperatures than raw water systems, allowing engines to run more efficiently while maintaining proper internal clearances and combustion performance.
This thermostat is typically rated at 170°F–180°F, making it correct for engines equipped with heat exchangers. The kit includes the thermostat along with required seals and gaskets for a complete service, ensuring proper sealing and consistent coolant flow through the system.
Key Features
- Genuine Mercury MerCruiser / Quicksilver OEM kit
- Designed for closed cooling (freshwater cooled) systems
- Higher temperature rating (typically 170°–180°F range)
- Includes thermostat, seals, and installation gaskets
- Direct OEM replacement — no modification required
- Maintains optimal engine temperature and efficiency
Engine Compatibility
Fits GM-based MerCruiser engines equipped with closed cooling systems:
- 4.3L V6 (closed cooling models)
- 5.0L V8 (305)
- 5.7L V8 (350)
- 7.4L V8 (454)
- 8.2L V8 (502)
Applications include:
- MerCruiser Bravo sterndrive with closed cooling
- MerCruiser inboard engines with heat exchanger systems
✔ Specifically for freshwater/closed cooling systems
✔ Not for standard raw water cooled engines
Serial Number Fitment Notice
Fitment varies by engine serial number and cooling configuration. Always confirm using your engine serial number before ordering. Engines converted from raw water to closed cooling may require different thermostat kits.
When This Part Needs Replacement
- Engine running too hot or overheating
- Engine not maintaining consistent temperature
- Thermostat sticking or corrosion present
- Cooling system service or rebuild
- Preventative maintenance on closed cooling systems
Installation Notes
- Replace all included gaskets and seals during installation
- Ensure thermostat orientation is correct (spring side toward engine)
- Clean housing and sealing surfaces thoroughly
- Inspect heat exchanger and coolant passages for blockage
- Verify coolant condition and replace if contaminated
Alternate / Superseded / Cross-Reference Part Numbers
- Mercury / Quicksilver: 807252T4
- Supersedes / Related: 807252T3, 807252Q4
- Sierra: 18-3648
- EMP: Equivalent to 807252Q4
- Thermostat (internal): Higher temp variant (approx. 170°–180°F)
Parts Desk Insight
This kit is commonly used on MerCruiser engines equipped with closed cooling systems where higher operating temperatures improve efficiency and reduce internal wear. A common mistake is installing a 160°F thermostat (raw water version) into a closed cooling engine — this will cause improper engine operation. Always confirm cooling system type before ordering.
Shipping
Shipping: Ships same or next day for fast Canada wide shipping. ⚓
Shipping information
In-stock and OEM parts: ship same or next business day.
Locally warehoused items: ship within 3–4 business days.
Special-order items: timeline confirmed after order.
Returns & warranty
Returns & Satisfaction Guarantee
We stand firmly behind the quality of every product we sell. Your confidence matters to us — and we back it with a straightforward 30-Day Satisfaction Guarantee.
If you are not fully satisfied, you may request a return within 30 days of delivery. All returns must receive pre-approval prior to being sent back. Unauthorized returns will not be accepted.
To qualify for a return:
Item must be in new, unused condition
Product must be in its original packaging
All parts, components, hardware, manuals, and accessories must be included
Packaging must be undamaged and suitable for resale
Important:
Electronics are strictly inspected. No returns on open-box electronics. Exceptions may apply only with prior written approval. Any electronic unit that has been installed, powered, activated, or altered may not be eligible for return.
We are serious about product integrity — and equally serious about taking care of our customers. If there is ever a product issue, contact us immediately so we can make it right.
For return authorization, please contact our support team before shipping anything back.