Cooling methods are provided for facilitating pumped immersion-cooling of electronic components. The cooling method includes: providing a housing forming a compartment about one or more components, and providing a supply manifold, a return manifold, and coupling a coolant loop coupling in fluid communication the supply and return manifolds and the housing. Coolant flowing through the coolant loop flows through the compartment of the housing and, at least partially, immersion-cools the component(s) by flow boiling. A pump facilitates circulation of coolant within the loop, and a coolant bypass line is coupled between the supply and return manifolds. The return manifold includes a mixed-phase manifold section, and the bypass line provides coolant from the supply manifold directly to the mixed-phase manifold section. Coolant flows from the coolant bypass line into the mixed-phase manifold section in a direction counter to the direction of any coolant vapor flow within that manifold section.