An expansion tank (10) for a vehicle cooling system (18) of an engine using a liquid coolant (16) includes a tank body (12) defining a first volume (V1) containing coolant (16), wherein the coolant defines a variable coolant elevation level (CEL) within the tank body. The tank body (12) also defines an upper volume (20) containing air. A bladder (14) is disposed in the tank body (12) and defines a second volume (V2) containing air. The bladder (14) includes a flexible membrane (36) actuated by an actuator (46). When the engine is stopped or is below a predetermined temperature, the flexible membrane (36) is moveable to a first position (FP) which lowers the coolant elevation level (CEL), and when the engine is started or reaches a predetermined temperature, the flexible membrane (36) is moveable to a second position (SP) which raises the coolant elevation level. A communicating line (38) is in fluid communication between the upper volume (20) and the second volume (V2) to fluidly communicate air therebetween.