A cooling system for an engine system includes an engine coolant path inside an internal combustion engine and a turbine coolant path inside a turbocharger. A switching section is selectively switched to one of a first operation mode, in which coolant in the cooling system is permitted to flow through the engine coolant path and the turbine coolant path, and a second operation mode, in which the coolant in the cooling system is permitted to flow only through the engine coolant path, while not being permitted to flow through the turbine coolant path. When the switching section is in the first operation mode and a basic flow rate calculated based on an engine operating state is larger than an actual flow rate detected by a flow rate sensor by at least a determination amount, the switching section is switched to the second operation mode.