Sounds like you got a leak - need repair
there is supposed to be water in the radiator. your radiator is supposed to be evenly mix 50/50 with radiator fluid and water, preferably distilled water.
There is a water reservoir tank that goes to the radiator that you can add the water to.
If the radiator is not being pressurized from exaust than it should. As long as the coolant is going out of the system either in the oil or out the exaust it has always worked for me. If exaust is getting into the coolant the liquid glass has no chance to plug the leak. With the engine cold, take the radiator cap off and crank the motor. You will know quickly if it will work. Water either shoots out the radiator or doesn't.
Radiator coolant.
You can add water to a radiator any time it is low on water.
remove your radiator form your car then poor some hot water in radiator till water comes out nice and smooth.
The radiator cools the water which then goes to your engine to cool it off, as cool water enters your engine hot water from the engine enters your radiator
Bidet
The water is boiling in radiator because it's temperature(radiator's) reaches the boiling point of water when the engine works for a long time.
When a car is hot, keep the car running and add water to the radiator. When a car is cold, you can simply put the water into the radiator.
radiator fluid
To add water to the radiator on a new beetle, first remove the lower radiator hose. Then add water to the coolant reservoir.