The radiator cap might need replacing.
You may have a bad head gasket and it may be leaking from that. Why when cold i dont know, but if you are losing coolant it may be the head gasket.
if you dont see any leaks its going into the motor. head gaskets, cracked block or heads etc etc
NO additives are recommended by any good mechanics. Only the full repair is best especially whem dealing with coolant leaks. Usually intake leaks are from years of corrosion the coolant will turn to acid in most oif todays cars if not treated you will have much internal damage. the external leaks will only show up when damage is done. Dont write off the vehicle it ,will be much cheaper to repair than pay the extra cost for insurance ,interest loss of value for new cars.....
My 1997 Cadillac Catera does the samething! Normally can be done by the Coolant leaking ,Coolant needing to be flushed, a PCV Valve, Coolant Temperature Sensor, Themostat Sticking, oil cooler, and the list goes on. . You should most likely have a "Experienced" Mechanic look at the vehicle to do a pressure test to make sure you dont have any leaks and to see what is actually wrong.
old beetles dont use coolant
I dont no
Water should be fine, but mix it with coolant when you can to prevent rust from developing in the radiator.
you need to add coolant to the coolant resevoir. coolant is antifreeze. if you dont have enough in your car you can overheat and damage your engine.
You dont Take it to a qualified mechanic for a flush and they will dispose of the old coolant You dont Take it to a qualified mechanic for a flush and they will dispose of the old coolant
i dont knowe the answer
20%
dont eat stupid