Coolant expansion tank and its plug

The expansion tank is located in the engine compartment, is made of white transparent plastic and has a spherical shape. In addition to the outlet hose at the level of the plug, it has a drain hose fitting.

There is a device in the tank to control the level of the coolant. It operates on the principle of an electric current flowing between two electrodes while they are immersed in a coolant. As soon as the liquid level drops below the set level, the current will be interrupted and the driver will be indicated about the lack of coolant by a simultaneously lit indicator and a sound signal. In a similar way, the signal will also be received when the permissible operating temperature is exceeded (about 119°C) coolant. (Coolant thermometer on the dashboard of a classic type.)

The plug of the filler neck of the expansion tank is made of blue plastic, with a thread and an overpressure valve that opens at 0.14 MPa and a valve that opens with a vacuum that lets air into the tank when the liquid level drops during cooling. This valve operates within the reduced pressure range of 0.002–0.01 MPa. The reservoir and plug on all cars are the same, regardless of the type of engine.