[Jack21]

As water heats up, it expands. As it cools down, it contracts.

Some cooling systems leave air space at the top of the radiator to allow for this expansion & contraction. Others, like your Cobra & mine have a coolant recovery system so the hot coolant can puke into the recovery tank when hot, and suck back into the engine when cool. Mine "Breathes" about 1/2 qt in and out of the engine. Am using a Stant 7# cap to avoid pressure build up that might push a hose off one of the crossover tubes. Thermostat is 180 deg year round.