Sierra 18-3557 143 Degree Marine Thermostat, White, Replaces Volvo Penta 21148403

The Sierra 18-3557 is a 143 degree marine thermostat engineered to regulate engine coolant flow and keep your marine engine operating at the correct temperature range for efficient combustion and reduced wear. It is a white, plastic-bodied thermostat sized for direct fitment as a replacement engine cooling component, correcting overheating or slow-warm-up issues caused by a stuck, corroded, or failed factory thermostat. Installing a fresh thermostat is one of the most common and effective ways to restore proper engine temperature control and protect against overheating damage to gaskets, hoses, and engine internals.

The 18-3557 cross-references directly to Volvo Penta OE part number 21148403, giving boat owners and marine technicians a straightforward aftermarket alternative to the OEM part. It is sold as a standalone thermostat and is compatible with cooling systems designed around the referenced Volvo Penta OE number.

Specifications

• Brand: Sierra
• Manufacturer Part Number: 18-3557
• Temperature Rating: 143 Degrees F
• Color: White
• Material: Plastic
• Weight: 0.05 pounds
• UPC: 030999563019
• OEM Cross Reference: 21148403

Fitment

• Volvo Penta engines using OE part number 21148403

Replaces (OEM)

• 21148403

Frequently Asked Questions

What temperature rating is the Sierra 18-3557 thermostat? The Sierra 18-3557 is rated to open at 143 degrees Fahrenheit, which regulates when coolant begins circulating through the engine.

What OEM part does the Sierra 18-3557 replace? It replaces Volvo Penta OE part number 21148403, making it a direct cross-reference for that engine cooling application.

What is the Sierra 18-3557 made of? This thermostat has a white, plastic housing designed for durability in a marine engine cooling system.

How much does the Sierra 18-3557 thermostat weigh? The Sierra 18-3557 weighs 0.05 pounds.

Is the Sierra 18-3557 a genuine Volvo Penta part or aftermarket? The 18-3557 is a Sierra-manufactured aftermarket thermostat built to replace Volvo Penta OE number 21148403, not a Volvo-branded part.

What comes in the box with the 18-3557? The Sierra 18-3557 ships as a standalone thermostat unit.

Can I use the 18-3557 as a routine maintenance replacement? Yes, replacing a thermostat like the Sierra 18-3557 on a routine or preventive basis, or at the first sign of overheating or slow warm-up, helps maintain proper engine temperature control.

Does the Sierra 18-3557 fit any thermostat housing? The 18-3557 is designed for engines that originally used Volvo Penta OE part 21148403; confirm your existing thermostat's part number matches before ordering.

What color is the Sierra 18-3557 thermostat? It is white in color with a plastic body.

How do I know if my thermostat needs replacing? Symptoms like engine overheating, slow warm-up, or fluctuating temperature gauges often indicate a failed thermostat, and installing a Sierra 18-3557 is a common fix when your engine uses the 21148403 reference.

Is the Sierra 18-3557 the same as other Sierra thermostats? No, the 18-3557 is a distinct Sierra part number specifically cross-referenced to Volvo Penta 21148403; other Sierra thermostat part numbers correspond to different OEM applications.