Cooling system in a vehicle

A cooling system in a vehicle, wherein the vehicle includes a combustion engine, and wherein the cooling system comprises:

• a cooling fluid pump configured and operable to circulate cooling fluid in the cooling system, a cooler for cooling the cooling fluid, and a valve that is configured and operable to lead cooling fluid to the cooler for cooling or to a return line without cooling;
• a first circuit comprising cooling channels configured and operable for cooling of the combustion engine, said first circuit being configured and operable for leading cooling fluid from the cooling fluid pump to a first inlet at the valve;
• a second circuit configured and operable for the cooling of a hydraulic retarder, the second circuit being configured and operable to lead cooling fluid to a second inlet at the valve;
• the second circuit being configured and operable to receive cooling fluid from the first circuit at a receiving position that is located downstream of the cooling fluid pump and upstream of the cooling channels of the combustion engine, and the valve is configured and operable to block, in operating conditions in which the hydraulic retarder is not activated, the second inlet and thus to block the circulation of cooling fluid through the second circuit at the same time that the valve receives cooling fluid from the first circuit through the first inlet.