A thermostat arrangement for a cooling system for a motor vehicle, which thermostat arrangement comprises: • an inlet channel intended for the reception of cooling fluid that has circulated around a combustion engine of the motor vehicle, • a first outlet channel that is connected to the said inlet channel and from which cooling fluid is intended to be led to a cooler of the said cooling system, • a second outlet channel that is connected to the said inlet channel and from which cooling fluid is intended to be returned to the combustion engine without passage through the said cooler, • a valve body that can be displaced between different positions for the regulation of the flow of cooling fluid from the said inlet channel to the said outlet channels (5, 6), • a temperature-dependent activation element, and • a part that can be displaced designed such that during displacement of the same it carries with it the valve body, whereby the activation element is arranged to influence the displaceable position of the said part and thus of the valve body depending on the temperature of the cooling fluid that is received through the said inlet channel, whereby the valve body demonstrates a valve device in the form of a first plate element that when at a first end position of the valve body is in contact with a valve seating between the inlet channel and a second plate element that forms the first outlet channel in order to prevent through this contact cooling fluid from flowing from the inlet channel to the first outlet channel, and whereby the first plate element is arranged such that it can be displaced under the influence of the activation element away from its contact with the second plate element in order to open a connection between the inlet channel and the first outlet channel, whereby the two plate elements (15, 16) are designed to form on displacement of the same away from the said position of contact the said connection in the form of a section of channel defined by surfaces (23, 24) of the two plate element (15, 16) that are turned to face each other and demonstrate flow-retarding forms, characterised in that the said flow-retarding forms comprise the said surfaces (23, 24) that essentially follow each other when in the said position of contact, that the said surfaces (23, 24) define an extent of the section of channel that forms the said connection that extends the flow pathway and in that the said surfaces (23, 24) of the plate elements (15, 16) demonstrate wave-shaped forms that essentially follow each other when in the position of contact in order to form during the opening phase of the opening of the said connection a wave-shaped meandering section of channel between the inlet channel and the first outlet channel. • an inlet channel intended for the reception of cooling fluid that has circulated around a combustion engine of the motor vehicle, • a first outlet channel that is connected to the said inlet channel and from which cooling fluid is intended to be led to a cooler of the said cooling system, • a second outlet channel that is connected to the said inlet channel and from which cooling fluid is intended to be returned to the combustion engine without passage through the said cooler, • a valve body that can be displaced between different positions for the regulation of the flow of cooling fluid from the said inlet channel to the said outlet channels (5, 6), • a temperature-dependent activation element, and • a part that can be displaced designed such that during displacement of the same it carries with it the valve body,