Thermostat malfunction (Mercedes-Benz Sprinter 903)

The thermostat will not open if it is jammed or the valve is stuck. In this case, even if the temperature gauge is already in the red zone, the radiator remains cold. Wait until the engine cools down, then unscrew the thermostat housing and remove it. You can drive for some time without a thermostat - this will not harm the engine. Operating your vehicle with a faulty thermostat can cause serious engine damage. Thus, the cylinder head gasket may burn out, the cylinder head may become deformed or even crack.

The thermostat does not close completely if a foreign object gets in. A sign of this malfunction is, for example, heating of the radiator immediately after starting a cold engine. The engine warms up very slowly. It is necessary to replace the thermostat as soon as possible, since its malfunction leads to increased fuel consumption and can damage the engine, which does not warm up to operating temperature.