Comparing 16 PSI Radiator Cap to Carbonated Soda Can Pressures

When you loosen a radiator cap on a cooling system that is at or above 212 F. The pressure in the system drops to atmospheric pressure and the liquid coolant flashes to steam. When water flashes to steam its volume increases by a ratio of 1600:1
So 1 cu ft of water makes about 1600 cu ft of steam. That is where your "geyser" comes from.
It is the rapid expansion of the volume of the coolant changing states that creates the risk. That would also why a soda can at 16 psi is not a comparable situation.