Cooling System

Have you pressure tested the complete system, including cap? Think there is any chance of a blown head gasket? Has the radiator been flow tested? There are no block thermostats, correct? Main thermostat is not put in backwards?

Do you have an old pump to check for impeller orientation? On some applications, coolant has to be routed through the heater core. It acts as a safety bypass in case the WP bypass is defective in some manner.