Over flow bottle ???

If you want the system to work like a normal recovery system, you need a different type of cap. A regular cap only vents coolant out. S ecovery cap has a 2 way valve. When the radiator heats up and the colant xpands, it lets coolant drain to the bottle. When the system cools down, a sligh vaccum occurs in the cooling system and the cap will open again to let coolant from the bottle go back into the radiator.
This way you will never have to top off the radiator as it will always be fuul and the bottle will never go empty.

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"A coolant overflow tank, also known as a recovery tank or expansion tank, regulates the excess coolant that builds up in a car's engine as it heats up:

• Pressure
  When the engine heats up, the radiator cap allows excess coolant to escape into the tank to relieve pressure. The pressure spring in the cap seals the system until it reaches a certain pressure level.
  
  
  
  
• Coolant flow
  The coolant is transferred between the tank and the cooling system based on the pressure from the coolant.
  
  
  
  
• Coolant return
  When the engine cools down, the system creates negative pressure that draws the excess coolant back into the radiator.
  
  
  
  
• Coolant level
  When the engine is off, the coolant reservoir should be about 30% full. The cold level should be set low, and the full or hot mark should be where the coolant is when the engine is at its normal operating temperature.
  
  
  
  
• Coolant replenishment
  The reservoir is also where new coolant is added to the system.
  
  
  
  
• Coolant leaks
  A crack or leak in the reservoir can cause constant coolant replenishment and the possibility of overheating. "