Marine Thermostat & Its Role in the Engine Cooling System


Temperature management is essential to optimise engine health, performance, and efficiency for extended lifecycle. While vessel owners are cautious about the coolants and exhausts, the thermostat is often overlooked. A marine thermostat is a small device but an integral part of the engine’s cooling system.

We are offering a guide to marine engine thermostats here to demonstrate the importance of this device in the engine’s cooling unit.

What is a Thermostat in the Ship Engine

A marine thermostat is located within the thermostat housing (between the radiator and the engine) and held to its position with a fastener. Its prime function is to regulate the circulation of the coolant fluid (water or oil) across the engine’s cooling system. The temperature-reactive valve maintains the optimal engine operating temperature range (80o-88oC). This device is used in both 2-stroke and 4-stroke internal combustion engines and has a complex mechanism to ensure precise movement.

Here is a synopsis of the components of marine engine thermostat:

  • Primary Valve – allows cool water to flow to the radiator when the temperature surges above normal temperature
  • Bypass Valve – when the engine temperature rises, this valve closes to discharge the cooling water to the radiator
  • Wax Cylinder – this charge cylinder contains solid wax. The wax starts melting when the cooling water accumulates heat. The melted wax induces the secondary valve to close and uplifts the piston to open the main valve on the top.
  • Main Valve Gasket – restricts the primary valve from unwanted flow
  • Primary Spring – creates tension to close the primary valve when the temperature of the cooling water drops below the specified level
  • Secondary Spring – controls the retraction of the piston rod to a specific point, submerging it into the wax cylinder
  • Piston/Plunger – regulates the opening and closing of the thermostat valve

How Does the Marine Thermostat Works

The functioning of a marine engine thermostat is based on the principle of temperature sensing. The thermostat remains closed when the engine is cold below the operating temperature range. It allows the coolant fluid to flow throughout the engine block (except the radiator). This allows the engine to attain the operation temperature.

Conversely, when the engine temperature is higher than the operational temperature, it heats up the coolant fluid. The wax in the cylinder absorbs heat from the hot fluid and melts to push the piston upwards. This directs the hot fluid to the heat exchanger for cooling.

The thermostat is an optional but vital device for marine diesel engines. Without the interference of this valve the cooling system cannot transfer heat from the engine to the radiator.

Operating a marine engine without a thermostat poses a risk of damage due to overheating. Monitoring the t-stat regularly is essential to ensure it is working accurately.

Is Your Diesel Engine Overheating Frequently?

This may happen due to the thermostat failure. Fortunately, marine thermostats are easy to replace with a new piece to keep your engine healthy and running at its best.

Marine professionals always recommend replacing thermostats with OEM parts. For instance, if your Perkins engine is deliberately heating up, a genuine Perkins CH11620 replacement part can assure peace of mind.

Shop Marine Engine Thermostats from Top Global Brands

Alfa Marine Spare Parts is a one-stop online store for purchasing authentic marine engines and spare parts. We supply marine products from top brands – Caterpillar, Cummins, Volvo Penta, Bosch, Doosan, Komatsu, Scania, Wartsila, Yanmar, and more.

Invest in high-quality OEM marine spare parts for safety, guaranteed efficiency, and performance.

Browse our product catalogue to find the required diesel engine thermostat. Contact us with the spare part number if you do not find the matching item on the category page. Our knowledgeable sales representatives can arrange the shipping in 2-3 business days.

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