An end cap closes the open end of the tank. The end cap is comprised of an inlet diverter wall and tube diverter wall. The inlet diverter wall extends into the tank across the inlet axis for redirecting fluid from the inlet and longitudinally into the tank along the end of the core. The tube diverter wall also extends longitudinally into the tank in a spaced relationship to the tubes of the core for directing fluid out of the tubes and longitudinally into the tank. A first embodiment of the invention provides tube diverter walls that are planar. A second embodiment of the invention provides tube diverter walls that are curved.