| 摘要 |
An engine cooling system for an outboard motor includes a thermostat mounted on an upper surface of a cylinder block to open and close a cooling water passage depending on the temperature of cooling water inside the cooling water passage, and a relief valve mounted on an upper portion of a side wall of the cylinder block and located adjacent to the thermostat to open and close the cooling water passage depending on the pressure of cooling water inside the cooling water passage. Since the relief valve is located adjacent to the thermostat, the distance (length of an isolated portion of a drainage passage extending) between the thermostat and the relief valve is very small. In the case where the isolated drainage passage portion has no cooling water flowing therethrough, the pressure of the cooling water inside the cooling water passage rises until the relief valve is open. When the relief valve is open, the cooling water flows into the drainage passage with the result that a sufficient cooling effect can be attained over the entire area of the cooling water passage including the isolated drainage passage portion.
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