Steam and foam coming from radiator and overflow but not overheating Options

[mjzraz]

I can't figure out why I am still getting steam and foam out of the overflow but it's not overheating according to the gauge and a thermometer.
After working on this some more today, here is where I am. I flushed the cooling system with a coolant flush and drained and filled it twice with water to clear it out. I pushed water with the garden hose pressure through the top radiator hose and the heater core hoses with the thermostat removed until everything was clear. I reinstalled the thermostat and hoses and filled with antifreeze/water mix.

The book says 6 quarts total coolant. I was only able to get 3 quarts and it appeared full. I ran it to see if when the thermostat opened, the level would drop and I could add more. The problem is it really didn't let me put much more in and it keeps filling the overflow with bubbles and foam, then steam comes out of the overflow and it sounds like it is gurgling and boiling. If I run with the radiator cap off, it will spurt bubbles and coolant out the top of the radiator. Additionally the lower radiator hose that comes from the thermostat housing looks looks like it is vibrating as if the flow of water through it is not constant, but choppy. The thermostat is new and I tested it to make sure it opened fine in a pot of water on the stove.

Fearing the worst, that I somehow didn't fix the head gasket that was recently replaced, I bought a block combustion leak detector at Napa and tested the gasses at the radiator. It has a blue liquid that you draw up air through from the radiator and if there is combustion gas it will turn yellow. I tested and it did not turn yellow at all. I verified the test fluid was working, by inhaling some exhaust from the tailpipe and it turned yellow. So I believe I do not have a head gasket leak.

When I did the head gasket, the water pump showed no signs of leaking and I looked at the pump fins through the outlet pipe and also spun it and it felt fine. I always thought they should be replaced when they are noisy, leaky or had play in the shaft/pulley. Mine appeared fine based on that.

I have no idea what to try next. I feel like there might be a blockage or air in the system, but know of no way to clear or test for it.