Sierra 18-3552 Thermostat Mercury MerCruiser Replacement

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

Whats 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Alternate / Superseded Part Numbers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 thermostatif youre servicing a 4.3, 5.0, or 5.7, its one of the first cooling parts to replace