A compression ignition engine, comprising: an engine body having a cylinder where a combustion chamber is formed; a supercharger, configured to boost intake air to the combustion chamber of the engine body; and one or more valves configured to switch a state between a first state in which the intake air is boosted by the supercharger and a second state in which the intake air is not boosted by the supercharger, a fluid temperature adjuster (63, 81, 82) configured to adjust a temperature of engine coolant configured to be supplied to a radiator (62, 72) from the engine body to cool the engine body; and a controller configured to control operation of the engine body including operations of the one or more valves and the fluid temperature adjuster (63, 81, 82), wherein when the controller determines that an operating state of the engine body is in a high-load operating range where an engine load is equal to or more than a given load, the controller is configured to control the combustion mode to be in a compression ignition combustion mode in which an unburnt mixture gas is self-ignited during flame propagation combustion of a mixture gas caused by spark ignition inside the combustion chamber, wherein when the controller determines that the operating state of the engine body is in the high-load operating range, the controller is configured to cause the one or more valves to be in the first state, while when the operating state of the engine body is in a low-load operating range in which the load is lower than the given load, the controller is configured to cause the one or more valves to be in the second state, and wherein when the controller determines that the operating state of the engine body is in the high-load operating range, the controller is configured to output a control signal to the fluid temperature adjuster (63, 81, 82) so that a target temperature of the engine coolant is lowered, compared with the case when the operating state of the engine body is in the low-load operating range, wherein the fluid temperature adjuster (63, 81, 82) has an air amount adjuster (81, 82) configured to adjust an amount of air passing through the radiator (62, 72), wherein the air amount adjuster (81, 82) include a grille shutter and a radiator fan configured to send air to the radiator (62, 72), and wherein when the operating state of the engine body is in the high-load operating range, the controller is configured to increase the amount of the air adjusted by the air amount adjuster (81, 82) by increasing an opening of the grille shutter and a rotational speed of the radiator fan, compared with the case when the operating state of the engine body is in the low-load operating range. an engine body having a cylinder where a combustion chamber is formed; a supercharger, configured to boost intake air to the combustion chamber of the engine body; and one or more valves configured to switch a state between a first state in which the intake air is boosted by the supercharger and a second state in which the intake air is not boosted by the supercharger, a fluid temperature adjuster (63, 81, 82) configured to adjust a temperature of engine coolant configured to be supplied to a radiator (62, 72) from the engine body to cool the engine body; and a controller configured to control operation of the engine body including operations of the one or more valves and the fluid temperature adjuster (63, 81, 82), wherein when the controller determines that an operating state of the engine body is in a high-load operating range where an engine load is equal to or more than a given load, the controller is configured to control the combustion mode to be in a compression ignition combustion mode in which an unburnt mixture gas is self-ignited during flame propagation combustion of a mixture gas caused by spark ignition inside the combustion chamber, wherein when the controller determines that the operating state of the engine body is in the high-load operating range, the controller is configured to cause the one or more valves to be in the first state, while when the operating state of the engine body is in a low-load operating range in which the load is lower than the given load, the controller is configured to cause the one or more valves to be in the second state, and wherein when the controller determines that the operating state of the engine body is in the high-load operating range, the controller is configured to output a control signal to the fluid temperature adjuster (63, 81, 82) so that a target temperature of the engine coolant is lowered, compared with the case when the operating state of the engine body is in the low-load operating range, wherein the fluid temperature adjuster (63, 81, 82) has an air amount adjuster (81, 82) configured to adjust an amount of air passing through the radiator (62, 72), wherein the air amount adjuster (81, 82) include a grille shutter and a radiator fan configured to send air to the radiator (62, 72), and wherein when the operating state of the engine body is in the high-load operating range, the controller is configured to increase the amount of the air adjusted by the air amount adjuster (81, 82) by increasing an opening of the grille shutter and a rotational speed of the radiator fan, compared with the case when the operating state of the engine body is in the low-load operating range.