Coolant loop for a combustion engine

The refrigerant circuit (1) has a cylinder crankcase (3) with two opposite-lying cylinder banks (3a,3b) and associated cylinder heads (4a,4b). The cylinder crankcase and the cylinder heads are impinged with coolant over separated partial circuits (5,6) of the refrigerant circuit. The partial circuits run parallel to each other. A check valve (9) is arranged in the cylinder crankcase-partial circuit, which allows a flow of coolant only from the inlet side to outlet side through the cylinder banks.