A cooling system for an engine includes a block-side water jacket divided into a block cooling passage and a bypass passage in the circumferential direction of the block-side water jacket, the block cooling passage allowing a cooling liquid introduced into the block cooling passage to flow into the head-side water jacket via a first communication hole of a cylinder head, and the bypass passage allowing the cooling liquid to bypass the block cooling passage and flow into the head-side water jacket via a second communication hole of the cylinder head. The cooling system further includes a partition separating a downstream end of the block cooling passage and the bypass passage from each other in the circumferential direction. The partition is provided with an adjustment hole which makes a flow of part of the cooling liquid passing through the bypass passage directed to the first communication hole.