A thermostat valve arrangement for the cooling circuit of an internal combustion engine includes a main valve member movably mounted in a housing adapted to be pressed against a main valve seat by a spring. The valve arrangement further includes a bypass valve member cooperating with a bypass valve seat in the housing. An expansion element has a first section cooperating with an abutment fixed to the housing and a second section cooperating with the main valve member and the bypass valve member such that the main valve or bypass valve is selectively closed and/or opened, in order to produce the cooling circuit of the internal combustion engine by means of a radiator or a bypass.