I've just replaced the coolant and the coolant clamps. I've reinstalled the thermostat. I've also bled the system.
The original radiator cap was put back on.
So far I don't see any leaks from the thermostat housing. Nor from the radiator.
However, there's this rhythmic sound, and I think it's coming from the front of the engine.
Here's a video of the rhythmic sound.
Last oil check was last week. No top up was necessary.