Thermostats

The thermostat regulates the operating temperature of your marine diesel engine: it keeps the coolant in the engine block until the engine reaches operating temperature and then gradually opens. If the thermostat remains stuck closed, the engine will overheat — risking head gasket failure. If it remains stuck open, the engine never reaches operating temperature: fuel consumption increases, it fouls faster, and wear and tear accelerates. Both malfunctions are simply caused by material fatigue over the years.

Not sure about your thermostat? Testing is simple: place it in a pan of water and heat it slowly. The thermostat should open at the temperature stamped on it (for example 71 °C). If it does not open, opens too late, or does not open fully, replacement is the only solution — repairing is not possible and a new thermostat is inexpensive.

In this category you will find thermostats, thermostat housings, and water flanges for Beta Marine (Beta 28, Beta 30, Beta 43, Beta 50), Nanni (N3.30, 4.105 HE, N4.50), and Universal (M-25XPB). Each product specifies the applicable engine code, diameter, and opening temperature.

Does the engine still run too hot with a new thermostat? Then check the impeller, the heat exchanger, and the circulation pump, and monitor the temperature with a working temperature switch. If the engine has previously suffered severe overheating, also check the head gasket.