Water pump engine mount 440

not sure how you have the hoses all ran but, my 440 use to get air bound pretty easy.
I had all the heater hoses off and plugged all the holes. I use to drill a couple 1/8 in holes in the t stat to let air out. I would even pull one of the plugs when filling it. did it sit with straight water in it for a while? or half full? that's an odd water mark on the impeller of that water pump.