Van using large amounts of coolant

If you need a second opinion have a repair shop pressurize the cooling system and inspect for leaks. Any repair shop will have a cooling system pressurizing tool (it looks like a bicycle pump with a pressure gauge attached to it. It attaches to where the radiator cap is located on the radiator.) A blown headgasket may allow compression into the water jackets in the engine and or allow coolant into the cylinders, or it may not seal the water jackets and allow coolant to drip down the side of the engine block. A chemical test called "a block check" will test for the presence of carbon monoxide (a by product of engine combustion) in the cooling system which would definitely show that the head gasket is blown.