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.

 

You could have a blown head gasket. Look for a puff of white smoke when you first start up. Check the compression to confirm.
Back flushing the block can blow the seals on the water pump if done at too much pressure (like full city water pressure), so you may need to replace the water pump anyway.