The water passages in the cylinder block andcylinder head form the engine water jacket. In the cylinder block, the waterjacket completely surrounds all cylinders along their full length. Within thejacket, narrow passages are provided between the cylinders for coolantcirculation around them. In addition, water passages are provided aroundthe valve seats and other hot parts of the cylinder block. In the cylinderhead, the water jacket covers the combustion chambers at the top of the cylindersand contains passages around the valve seats when the valves are located in thehead.

The passages of the water jacket are designed to control circulation of coolantand provide proper cooling throughout the engine. The pump forces coolantdirectly from the lower radiator tank connection into the forward portion ofthe cylinder block. This type of circulation would, obviously, coolthe number one cylinder first; causing the rear cylinder to accept coolantprogressively heated by the cylinders ahead. To prevent this condition, theL-head block is equipped with a coolant distribution tube that extends fromfront to rear of the block, having holes adjacent to (and directed at) thehottest parts of each cylinder. I-head engines are equipped with ferrule typecoolant directors that direct a jet of coolant toward the exhaust valve seats