Marine vessel and marine engine cooling system

A marine vessel comprising:

• a hull;
• an engine in the hull and including an exhaust manifold, a cylinder head, and a cylinder block;
• a cooling flow passage to allow cooling water to flow therethrough to cool the engine;
• and
• a thermostat in a vicinity of or adjacent to a cooling water outlet of the cylinder block to adjust a flow rate of the cooling water discharged from the cylinder block based on a temperature of the cooling water;
• wherein
• the cooling flow passage is operable to allow the cooling water that has flowed through the exhaust manifold to flow into the cylinder block via the cylinder head and to allow the cooling water to flow into the cylinder block from a lower side of the cylinder block via a lower end flow passage port in a vicinity of or adjacent to a lower end of a flow passage portion in the cylinder block.