Estee wrote:
Hoe sê?
[/quote]

If you pressure the cooling system at 100 kPa (standard atmosphere pressure - essentially unpressurized), the water will boil at 100C, or ~375K.
But, if you raise the pressure to 1MPa (10 atmospheres), then you raise the boiling point by ~75C/K. But if you pressurize it to 1MPa and the temperature goes above boiling, then the pressure will spike, and the vessel will rupture. So you pressurize it to 1MPa and put in a relief valve for somewhere between that and rupture pressure of the container. If you get boiling, the pressure is released and nothing breaks.
That’s why they have a mix of pressurization and pressure relief.
In an automotive cooling system, boiling occurs. Not the whole system, and often not enough to cause over-pressure. But spot heating as it passes through the hotter parts of the engine will cause localized boiling, and that heat gets moved away, but being under-pressure it condenses as soon as the over-temperature condition passes.
With an overflow bottle, the over-pressure blows past the pressure-relief valve and goes into the overflow. When the pressure drops inside the system, it pulls the overflowed coolant back in.
Releasing pressure not only prevents the system from exploding, but causes cooling in that expansion causes cooling, though bubbles in the system do more harm than good for efficient cooling.[/quote]
Hemelsbreed verskillend van dit wat jy in post #2 probeer oordra het...
So wanneer sou jy sê, rofweg jaargetal/dekade, het die radiators van voertuie pressurized geraak...