An expansion tank system for a liquid cooling system includes a first chamber for receiving a coolant, a second chamber for pressurized gas, a first gas conveying device for conveying gas from the first to the second chamber, a second gas conveying device for conveying gas from the second to the first chamber, a first pressure sensor in fluid communication with the first chamber, and a control unit connected to the first gas conveying device, the second gas conveying device and the first pressure sensor for controlling the second conveying device to selectively convey gas from the second to the first chamber if a pressure measured through the first pressure sensor is below a predefined first threshold value, and for controlling the first conveying device to convey gas from the first to the second chamber if a pressure measured through the first pressure sensor is above a second threshold value.