An engine cooling structure for cooling an engine body including a plurality of cylinders by using a coolant, the engine cooling structure comprising: a cylinder block including: a block inner peripheral wall defining the plurality of cylinders; and a block outer peripheral wall surrounding the block inner peripheral wall to define a water jacket through which the coolant circulates between the block outer peripheral wall and the block inner peripheral wall; a spacer housed in the water jacket; and a cooler (63, 64) provided outside the engine body, wherein the block outer peripheral wall includes: a coolant inlet configured to introduce the coolant into the water jacket; and a coolant exit (16, 17) configured to lead out the coolant from the water jacket to the cooler (63, 64), the block inner peripheral wall includes an inter-bore part positioned between adjacent cylinders of the plurality of cylinders, the spacer includes: a peripheral wall surrounding the block inner peripheral wall; and a dividing wall protruding from the peripheral wall to divide the water jacket into an upper passage and a lower passage (21d, 22d) below the upper passage, the coolant inlet is provided at a position to introduce the coolant into the upper passage, the upper passage allows the coolant introduced from the coolant inlet to pass through the inter-bore part, the coolant exit (16, 17) is provided at a position to lead out the coolant in the lower passage (21d, 22d) to the cooler (63, 64), and the cooler (63, 64) cools a predetermined cooling object by the coolant led out from the coolant exit (16, 17), wherein the coolant exit includes a first exit and a second exit provided at different positions on the block outer peripheral wall, the cooler includes a first cooler and a second cooler that cool different cooling objects, the first exit leads out the coolant in the lower passage to the first cooler, and the second exit leads out the coolant in the lower passage to the second cooler, characterized by: a water pump configured to discharge the coolant to the coolant inlet; and a second passage connecting the water pump and the second exit outside the cylinder block, wherein the second cooler is an oil cooler that cools a lubricant supplied to the engine body, and the oil cooler and a second flow regulating device are provided in the second passage, the second flow regulating device being configured to change a flow rate of the coolant that circulates through the second passage. a cylinder block including: a block inner peripheral wall defining the plurality of cylinders; and a block outer peripheral wall surrounding the block inner peripheral wall to define a water jacket through which the coolant circulates between the block outer peripheral wall and the block inner peripheral wall; a spacer housed in the water jacket; and a cooler (63, 64) provided outside the engine body, wherein the block outer peripheral wall includes: a coolant inlet configured to introduce the coolant into the water jacket; and a coolant exit (16, 17) configured to lead out the coolant from the water jacket to the cooler (63, 64), the block inner peripheral wall includes an inter-bore part positioned between adjacent cylinders of the plurality of cylinders, the spacer includes: a peripheral wall surrounding the block inner peripheral wall; and a dividing wall protruding from the peripheral wall to divide the water jacket into an upper passage and a lower passage (21d, 22d) below the upper passage, the coolant inlet is provided at a position to introduce the coolant into the upper passage, the upper passage allows the coolant introduced from the coolant inlet to pass through the inter-bore part, the coolant exit (16, 17) is provided at a position to lead out the coolant in the lower passage (21d, 22d) to the cooler (63, 64), and the cooler (63, 64) cools a predetermined cooling object by the coolant led out from the coolant exit (16, 17), wherein the coolant exit includes a first exit and a second exit provided at different positions on the block outer peripheral wall, the cooler includes a first cooler and a second cooler that cool different cooling objects, the first exit leads out the coolant in the lower passage to the first cooler, and the second exit leads out the coolant in the lower passage to the second cooler, characterized by: a water pump configured to discharge the coolant to the coolant inlet; and a second passage connecting the water pump and the second exit outside the cylinder block, wherein the second cooler is an oil cooler that cools a lubricant supplied to the engine body, and the oil cooler and a second flow regulating device are provided in the second passage, the second flow regulating device being configured to change a flow rate of the coolant that circulates through the second passage. a water pump configured to discharge the coolant to the coolant inlet; and a second passage connecting the water pump and the second exit outside the cylinder block, wherein the second cooler is an oil cooler that cools a lubricant supplied to the engine body, and the oil cooler and a second flow regulating device are provided in the second passage, the second flow regulating device being configured to change a flow rate of the coolant that circulates through the second passage.