A keel cooler having a standard header with an internal beveled bottom wall, with orifices on the inner wall of the exterior tubes extending into the header, the orifices being in the natural flow path of the coolant flow. The orifices are sufficiently large so as not to restrict the flow of coolant. A fluid flow diverter is additionally provided in the header of the keel cooler for facilitating coolant flow towards both the interior tubes and also towards the exterior tubes.