Motor vehicle fuel system having multiple fuel tanks

A fuel system of an engine has a first fuel tank, a second fuel tank, and a pump for pumping fuel from the tanks to the engine. A first valve mechanism is selectively operable to a first position that allows fuel to be pumped concurrently from both the first and second tanks to the engine, a second position that allows fuel to be pumped from the first tank, but not the second, and a third position that allows fuel to be pumped from the second tank, but not the first. A second valve mechanism is selectively operable to a first position that allows fuel to return from the engine concurrently to both the first and second tanks, a second position that allows fuel to return to the first tank, but not the second, and a third position that allows fuel to return to the second tank, but not the first.