Sierra 18-3552 Thermostat – Mercury MerCruiser Replacement
Free returns on all eligible orders
You have 30 days to request a return. All sale items are final sale.
The Sierra 18-3552 Thermostat is a high-quality aftermarket replacement designed for Mercury MerCruiser engines, providing reliable temperature regulation and consistent cooling system performance.
Engineered to meet or exceed OEM specifications, this thermostat ensures proper engine warm-up and maintains optimal operating temperature, helping prevent overheating and improve fuel efficiency. Built with marine-grade materials, it delivers dependable performance in both freshwater and saltwater environments.
Key Features
- Sierra premium aftermarket replacement
- Meets or exceeds OEM specifications
- Maintains proper engine operating temperature
- Ensures efficient cooling system performance
- Corrosion-resistant marine construction
Engine Compatibility
Mercury MerCruiser Engines
Commonly used on:
- 4.3L V6 engines
- 5.0L V8 engines
- 5.7L V8 engines
➡️ Fits many GM-based MerCruiser sterndrive and inboard applications
Serial Number Fitment Notice
Fitment depends on:
- Engine model and year
- Cooling system configuration
⚠️ Always confirm compatibility using your engine serial number before ordering.
Specifications
- Part Number: 18-3552
- Type: Engine thermostat
- Function: Regulates coolant temperature
- Construction: Marine-grade metal housing
What’s Included
- Thermostat (gasket sold separately unless specified)
When This Part Needs Replacement
Replace the thermostat if you notice:
- Engine overheating
- Engine running too cold
- Fluctuating temperature readings
- Poor fuel efficiency
Installation Notes
- Replace gasket or seal during installation
- Ensure correct orientation
- Inspect housing for corrosion or debris
- Test cooling system after installation
Alternate / Superseded Part Numbers
OEM Cross References
- Mercury MerCruiser: 807252T1 / 807252Q5 / 853213
Aftermarket Cross References
- Sierra: 18-3552
Shipping
Shipping: Ships same or next day for fast Canada wide shipping. ⚓
💡 Parts Desk Insight
This is a very common MerCruiser thermostat—if you’re servicing a 4.3, 5.0, or 5.7, it’s one of the first cooling parts to replace 👍
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.