Well I read that usually the air gets trapped in your heater core
in passenger compartment.  And sometimes You need to elevate the front
of your car to put the heater core at a lower point.  Try jacking up
the front of your car as high as you can and put in on jack stands, and
chock the wheels, put in park and set emergency brake.  By the way park
usually only locks the driving wheel which in a front wheel car is only
front wheels, and emergency brakes usually only lock the rear wheels.
   Or maybe you could park on a steep hill, make sure to put in Park,
set emergency brakes, and chock wheels.
   Then run car without cap to hiccup system and put on cap afterward.

   Also check if you put on thermostat backwards , it happens,
temperature sensing wax pellet cylinder should face toward engine, also
if radiator cap will not hold pressure water will bubble into overflow,
change radiator cap.
    Also if with car cold and radiator cap removed, if water geysers
out almost as soon as you start car you usually have blown the head
gasket or cracked head since combustion pressure is being forced into
cooling system, since cooling system usually has a maximum pressure of
15 psi and combustion pressure is 150 psi.