Abstract: An outboard motor includes a cooling water passage that guides cooling water to cool an exhaust passage and a cylinder unit. A cooling water intake port draws external cooling water into the cooling water passage. A water pump draws cooling water into the cooling water intake port and supplies the cooling water to the cooling water passage. A thermostat is arranged in the cooling water passage downstream of the catalytic converter and the cylinder unit. A first bypass passage is connected to a first connecting section provided on the cooling water passage. The first connecting section is provided along the cooling water passage at a position farther downstream than the catalytic converter and farther upstream than the thermostat.

Abstract: An outboard motor includes an exhaust pipe that includes an outer wall section, an inner wall section, a coolant passage, and a constricted section. The inner wall section is arranged inward of the outer wall section. The coolant passage is arranged between the outer wall section and the inner wall section. The constricted section is configured to constrict a flow cross section of the coolant passage. A catalytic converter is housed in the exhaust pipe. A temperature sensor is installed in the constricted section and measures a temperature of a pipe wall of the exhaust pipe.

Abstract: An outboard motor can include a case that extends longitudinally and can be supported on a hull of a boat. An engine can be supported on the upper surface side of the case and a cowling can be supported on the upper end portion of the case for covering the engine from the outside. An idle exhaust passage can be formed to discharge exhaust produced during idling of the engine to the atmosphere from the inside of the case. An expansion chamber can be formed at a midway portion of the idle exhaust passage. The downstream end of the idle exhaust passage can serve as an idle exhaust port that is open to the atmosphere. A plurality of such idle exhaust ports can be formed.

Abstract: An outboard motor can include a case that extends longitudinally and can be supported on a hull of a boat. An engine can be supported on the upper surface side of the case and a cowling can be supported on the upper end portion of the case for covering the engine from the outside. An idle exhaust passage can be formed to discharge exhaust produced during idling of the engine to the atmosphere from the inside of the case. An expansion chamber can be formed at a midway portion of the idle exhaust passage. The downstream end of the idle exhaust passage can serve as an idle exhaust port that is open to the atmosphere. A plurality of such idle exhaust ports can be formed.