I had a cracked head on mine all last season and it didn't use near that amount of coolant. My GMC rad was designed to run with a pressure cap and without pressure it will lose coolant. I run a 7 lb cap and it doesn't lose any coolant. I think the tank of the radiator is not large enough to run without pressure. When I was burning some with the cracked head the only evidence was the color of the center insulator on that sparkplug. It also created a miss at low rpm.
