The workaround is the same as with the three cylinders: Have a telltale vent at the top of the cylinder block (one for each bank?) that serves the dual purpose of venting air and verifying water flow. My suspicion is (but I am no expert on these) that if the cooling system is in good order there is enough flow to push the air pockets down and out. But if the pump is marginal (impeller) or the thermostat/pressure regulator is not in good order there is potential for air lock.
On my V4 the telltale is plumbed into an existing 1/8″ pipe thread port that was originally used for a water heated choke, but this is inferior to a port at the top of the water jacket(s).
For what it’s worth, the same problem exists in many modern cars where the radiator cap is not at the high point of the system. It works until the head gasket begins to leak gasses into the water jackets, or…. A robust cooling system should always be able to vent non-condensible gases from the highest point.
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