Bro get it immediately. U can find easily. Go to the area of kabar market of cars / bilal gunj. Actually when the radiator liquid reaches a specific temperature n expands, some of the liquid comes to this reservoir ( thats why the reservoir isnt to be completely filled and is only to be filled upto the 'max' mark on it'. When cooling of the liquid thru radiator fan is achieved the expanded liquid contracts and goes back to radiator. At present ur radiator cant work properly and in this condition God forbid u can heat up the engine in summers. Also must use coolant for the radiator not normal water to avoid corrosion in the radiator and water body!! Stay happy!