4x4 Action Group

A lot of vehicles dont have the radiator cap anymore as I think its due to the cooling system now being pressurised, which raises the boiling point of the water allowing for higher engine temps? I think?

The older design which wasnt pressurised? has the radiator cap and a press on type expansion tank cap. The expansion tank caps on the newer system are the screw on pressure cap type. Again, I think this is the reason

Cooling systems has always been pressurised for the reason explained above. The vehicles without normal radiator caps are usually designed this way because the highest part of the radiator is lower than the highest cooling channel in the engine. Moving the pressure cap to the expansion reservoir raises the filling point and stops the loss of coolant when opening while reducing the possibility of air locks in the system

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Estee wrote:A lot of vehicles dont have the radiator cap anymore as I think its due to the cooling system now being pressurised, which raises the boiling point of the water allowing for higher engine temps? I think?

The older design which wasnt pressurised? has the radiator cap and a press on type expansion tank cap. The expansion tank caps on the newer system are the screw on pressure cap type. Again, I think this is the reason

Hoe sê?

[/quote]
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.

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...