Sierra 18-3687 Thermostat for Suzuki Outboard Engines

The Sierra 18-3687 is a replacement thermostat engineered for Suzuki outboard engines, helping regulate engine coolant temperature so the powerhead runs within its intended operating range. A properly functioning thermostat is a small part with an outsized job: it opens and closes to control coolant flow, preventing the engine from running too cold (which hurts fuel economy and combustion efficiency) or too hot (which risks overheating damage to gaskets, seals, and internal components). This unit is sized for a direct fit in the Suzuki outboard cooling system and is built by Sierra, a long-standing supplier of marine replacement parts trusted for its focus on boat-specific engineering rather than repurposed automotive components.

At 2 x 1.2 x 1.9 inches and 0.11 pounds, the 18-3687 is compact and lightweight, consistent with the small in-line thermostats used in outboard cooling circuits. It is intended as a straightforward swap for a worn, stuck, or failed thermostat during routine cooling system maintenance or when troubleshooting overheating or slow warm-up symptoms on a Suzuki outboard.

Specifications

• Brand: Sierra
• Manufacturer Part Number: 18-3687
• Product Type: Thermostat
• Application: Suzuki outboard engines
• Product Dimensions: 2 x 1.2 x 1.9 inches
• Weight: 0.11 pounds
• UPC: 808282383299

Fitment

Designed for use in Suzuki outboard engine cooling systems.

Frequently Asked Questions

What engines does the Sierra 18-3687 thermostat fit? The Sierra 18-3687 is designed for use in Suzuki outboard engine cooling systems.

What are the dimensions of part number 18-3687? This thermostat measures 2 x 1.2 x 1.9 inches, a compact size typical of in-line outboard thermostats.

How much does the 18-3687 thermostat weigh? It weighs 0.11 pounds, making it a lightweight, easy-to-handle replacement part.

Is the Sierra 18-3687 a genuine Sierra part or aftermarket? It is a Sierra-branded thermostat, part number 18-3687, manufactured as a marine replacement part rather than a generic automotive substitute.

What does a thermostat do in a Suzuki outboard cooling system? A thermostat opens and closes to regulate coolant flow, keeping the engine within its proper operating temperature range and preventing overheating or excessive cold running.

What symptoms indicate the 18-3687 thermostat needs replacing? Overheating, slow engine warm-up, or fluctuating temperature readings are common signs a Suzuki outboard thermostat like the 18-3687 has failed or is stuck.

What is included when ordering the Sierra 18-3687? The listing includes one Sierra 18-3687 thermostat unit.

Can the 18-3687 be installed as a routine maintenance item? Yes, replacing the thermostat during scheduled cooling system maintenance on a Suzuki outboard is a common preventive step.

Is professional installation required for the Sierra 18-3687? Thermostat replacement on a Suzuki outboard, including installing part 18-3687, is typically done by a marine technician or an experienced DIY owner familiar with the engine's cooling housing.

Does the Sierra 18-3687 come with a gasket? The dossier for the 18-3687 covers the thermostat itself; buyers should confirm gasket needs separately when servicing the cooling system.