To safely operate an engine, by positioning the top of a rotational cutting blade so that it is exposed from an intake through space between discrete bars in water, and forcibly rotating the rotational cutting blade when a cylinder block of the engine is overheated.

A temperature sensor detects overheat condition of an engine, and drives a motor 35 through a control line 38. Driving of the motor 35 rotates each rotational cutting blade 33, and rotation of the blade 33 exposes the tip of the blade 33 in water from an intake 14 through space between connecting pieces 31, 31. Cloth or vinyl covering whole surface of a connecting pieces lid during exposing is broken and divided by the tip of the rotational cutting blade 33, and passage of external water between at least connecting pieces 31, 31 is formed, and therefore, cooling water restarted to be fed to the engine.