May be your T-valve has rusted and stopped working which caused it. Also check fan speed.
Install new T-valve & Radiator cap
But before that flush radiator, do radiator service & filled with coolant.
If gas kit will be blown, then there will be mixing of oil & water. Check oil cap, if there is moisture or white liquid present, then it is blown
Also check is there bubbles coming in Radiator or traces of oil in radiator, cap or coolant then it is gone.
If there is leakage, then even on parking or standing, water will reduce(Check floor/road under your car) Is there any water spot?
If u r changing radiator, then look for imported Aluminum radiator