Vehicle cooling circuit having a retarder or a hydrodynamic clutch

A vehicle cooling circuit, especially an engine cooling circuit, including a cooling medium pump and a vehicle drive engine and/or other heat-generating assembly cooled by means of the cooling medium. The circuit includes a hydrodynamic retarder with the working medium of the hydrodynamic retarder simultaneously also being the cooling medium of the cooling circuit, and the hydrodynamic retarder operating as the cooling medium pump. The secondary blade wheel is associated with a brake or a drive running counter to the drive of the primary blade wheel in such a way that it can optionally be fixed in a first operating state (braking operation) or be driven counter to the rotational direction of the primary blade wheel and, in a second operating state (pumping operation), can partially or completely be released such that it circulates at the speed of the primary blade wheel or at a specified speed difference slower than the primary blade wheel.