No heat

Probably the heater core in the back of the van. Some vehicles have multiple heater cores. If you no longer have heat, likely your coolant level is low and you could risk overheating. The brown fluid is likely water put in the radiator instead of coolant that has now rusted. Water generally will corrode parts faster than antifreeze. In addition, if you are in a cold climate and the outside temp drops below about 25, you risk popping freeze plugs or cracking the engine block.