Fig. 4.43. Expansion tank: 1 – safety ring; 2 – gasket; 3 – sensor; 4 – float with lever
The control system operates from a floating sensor installed in the expansion tank (Fig. 4.43). If there is insufficient coolant, the contact closes.
The cause of malfunction may be a burnt-out lamp, a broken sensor or a broken wiring.
(Information copied from the website: MercedesMan)
If the indicator lamp does not light when you turn on the ignition, it may be burnt out.
If the lamp does not turn off when the engine is started, but the coolant level is normal, then the sensor is faulty. This can be checked by disconnecting the contact from the sensor. If the lamp goes out, the sensor is faulty. Remove the sensor, check the float and other elements. Replace the sensor.
Loss of coolant
If a large amount of coolant is lost while driving, be sure to replenish the loss; in extreme cases, use water for this purpose.
With a large temperature difference (cold water - hot engine) the cylinder head may warp. When receiving the so-called "cold shock" the engine block may develop a microcrack. Therefore, before filling the liquid, let the engine cool down and find out the reason for the loss of coolant as soon as possible.