Compensation tank for coolant in a cooling system having at least two cooling circuits which are operated at different temperature levels, wherein an inner space of the compensation tank is divided into separate chambers (K 1, K 2, L 1, L 2) by partition walls (3a, 3b, 3c), comprising: a) a first coolant chamber (K 1) comprising a first inlet and a first outlet for connecting the first coolant chamber (K 1) to a first cooling circuit, b) a second coolant chamber (K 2) comprising a second inlet and a second outlet for connecting the second coolant chamber (K 2) to a second cooling circuit, c) a first passage opening in a partition wall separating the first and second coolant chambers (K 1, K 2), preferably in the lower region thereof, for enabling an exchange of coolant between the first and second coolant chambers (K 1, K 2), d) a second passage opening in a partition wall separating the first and second coolant chambers (K 1, K 2), preferably in the upper region thereof, for enabling an exchange of air between the first and second coolant chambers (K 1, K 2), e) a first air chamber (L 1), which communicates with the second coolant chamber (K 2) via a first overflow connection, f) a second air chamber (L 2), which communicates with the first air chamber (L 1) via a second overflow connection and a first pressure valve attached thereto and communicates with the external space via a second pressure valve, wherein g) the second pressure valve is configured for a relative opening pressure corresponding to a pressure difference between a relative opening pressure of the first pressure valve and a predetermined increased relative opening pressure, so that a pressure addition results between their relative opening pressures; wherein the first overflow connection comprises an opening in one of the partition walls and a channel formed by the partition wall and another wall. a) a first coolant chamber (K 1) comprising a first inlet and a first outlet for connecting the first coolant chamber (K 1) to a first cooling circuit, b) a second coolant chamber (K 2) comprising a second inlet and a second outlet for connecting the second coolant chamber (K 2) to a second cooling circuit, c) a first passage opening in a partition wall separating the first and second coolant chambers (K 1, K 2), preferably in the lower region thereof, for enabling an exchange of coolant between the first and second coolant chambers (K 1, K 2), d) a second passage opening in a partition wall separating the first and second coolant chambers (K 1, K 2), preferably in the upper region thereof, for enabling an exchange of air between the first and second coolant chambers (K 1, K 2), e) a first air chamber (L 1), which communicates with the second coolant chamber (K 2) via a first overflow connection, f) a second air chamber (L 2), which communicates with the first air chamber (L 1) via a second overflow connection and a first pressure valve attached thereto and communicates with the external space via a second pressure valve, wherein g) the second pressure valve is configured for a relative opening pressure corresponding to a pressure difference between a relative opening pressure of the first pressure valve and a predetermined increased relative opening pressure, so that a pressure addition results between their relative opening pressures;