what an amazing thread. Kudos to @MoizIrfan for the wonderful explanation.
I will take this opportunity to ask a couple more questions. I am restoring my Khyber whose thermostat had been removed and fan was "direct". Radiator was replaced 2 years ago and water body replaced 6,7 months ago. Car has barely completed 4000kms since the engine was recently overhauled and water body changed. It has been running on tap water. Now, I want to install the thermostat and get everything in running condition (AC/heater etc.). Since you have owned a khyber previously, need your recommendation on how to proceed step by step? Would you advise to change the radiator or just flush the entire system and then change the pipes only?