Sounds normal, if you had the rad full. When you shut it off without the coolant circulating the engine heat transfers to the coolant and it pukes. It's better to run with a tank as the rad will always be full cold or hot, more coolant less air, better cooling system. Just be sure to get an overflow tank with enough capacity to hold the coolant expelled during expansion. I put 3" X 10" tank on mine and it's not quite large enough.