The van over heats and all the coolant is gone in one day. Can't find a leak, can it be a head gasket

Yes. Have a leak down test performed.

Most likely cause of the problem is a sticking thermostat located at the top of the engine below one end of the upper radiator hose. If you're going to replace the thermostat, make sure to flush the radiator first and that it is not blocked by any rust.