Method and apparatus for operating a cooling fluid circuit of an internal combustion engine

A method of operating a cooling fluid circuit of an internal combustion engine for an automatic vehicle at cold start of said engine, said cooling fluid circuit including pump means, a heat storage and heat exchanger means for a cabin heating system, said heat exchanger means having a saturation point and being interconnected between said heat storage and said engine, which method comprises unloading said heat storage to transfer heat thereof to cooling fluid circulating in said cooling fluid circuit and operating said heat exchanger means so as to transfer at least some of the heat of the circulating cooling fluid to heating air of said cabin heating system, with said heat storage being unloaded in a first unloading phase during which the cooling fluid circulates in said cooling fluid circuit at a flow rate substantially at the saturation point of said heat exchanger means, and thereafter in a second unloading phase during which the cooling fluid circulates in said cooling fluid circuit at a flow rate reduced such that the temperature of the heating air entering the vehicle cabin remains at a substantially uniform level during said second unloading phase until said engine has reached a temperature sufficient to maintain said substantially uniform level.