A cooling system for a vertical, liquid cooled engine having a first passage for guiding cooling air to a cooling fan disposed above the engine, and a second passage for guiding the cooling air drawn by the cooling fan to flow past the engine and to be exhausted forwardly and downwardly of the engine. The first passage includes an air inlet defined rearwardly of the engine, and is defined by part of an engine hood, a vertical bracket plate erected behind the engine, and a partition extending from the engine hood over an upper surface of the engine. Devices accessory to the engine which are vulnerable to the heat are mounted in a space inside the first passage. The second passage is formed by an air guide cover enveloping the engine and cooling fan and defining an opening in a region opposed to the cooling fan. The air guide cover includes a front portion extending downwardly along the cylinder head. The second passage contains a liquid cooler disposed between an upper surface of the cylinder head and the air guide cover, and a muffler in an exhaust region the second passage. The first and second passages are interconnected through the cooling fan, and define a substantially airtight space from air intake end to exhaust end.