The most problematic cooling system component is the water pipe. The age and movement of the engine on its mountings can eventually lead to cracks, or their interior fabrics can deteriorate due to hot water.
Inspect them when the engine is cold. Any sign of wear or deterioration is a danger signal: the sudden loss of coolant from a burst hose can result in rapid overheating and a seized engine.
A worn or damaged hose should be replaced as soon as possible.
Before that, you need to drain the cooling system. Remove the radiator cap and open the radiator drain faucet. If there is no faucet, disconnect the bottom hose. If the coolant contains antifreeze that you wish to reuse, drain it into a clean container; do not discharge it on the road, which is toxic.
Before installing a new hose, make sure it is replaced correctly. Some have built-in curves and some have different inner diameters at each end. The old clip should also preferably be replaced with a worm drive that has a larger contact area and makes the seal more efficient.
Never overtighten any type of clip: it may cut into the rubber.
Once the hose has been replaced, turn off the radiator tap (or reconnect the bottom hose) and slowly refill with a water and antifreeze mixture.
When using the antifreeze to reuse the coolant, filter it through a fine cotton cloth or a plastic tea strainer. Replace the radiator cap and run the engine to operating temperature. Check for leaks and tighten the clip if necessary.
When the engine is cool, make sure the system is at the right level. Do not remove the pressure cap when the engine is hot. It will release a jet of scalding liquid.