My van started shooting water into the overflow. It was more like a blockage problem to me so here is what I have tried so far with no luck. I removed the thermostat to one make sure it was not stuck and also to make sure I had circulation. Problem continued the circulation seems slow to me not sure how fast it should circulate. So next I changed the lower rad. Hose and at that time flushed the block as well as the rad. Problem continues I am now about to replace the water pump. There is just not that much to a cooling system. I own an aircraft maintenance shop now we don't have radiators but I am a good mechanic.
I think you're on the wrong track. Suspect a leaking head gasket. There is a tool to check for combustion gases getting into the cooling system. It is a glass cylinder with two chambers partially filled with a dark blue liquid. Air is drawn from the radiator through the liquid. If combustion gases are present the liquid will turn bright yellow.