Why does a cooling system need to be pressurized?

In summary, the cooling system in a car needs to be pressurized to prevent water from boiling. Even if the temperature gauge doesn't show it, there may be hot spots that are above the boiling point of water, but the pressure keeps it from boiling. If the system ran at 190F without being pressurized, it would lose water through evaporation. Properly functioning systems should not have local boiling, but it may occur if there is blockage. Modern cars have electric fans to prevent this. Making a high pressure cooling system for cars would be costly and impractical, but it is used in water-cooled nuclear reactors.
  • #1
ISX
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Sorry about posting my pointless crap, I just wonder a lot about things lol.

I realize the cooling system is pressurized to keep the coolant from boiling, but what if you never see over 190F, ever. Would the pressurized cap have any benefit in that case? Someone told me once about how even though you might never see it on the gauge, there are hot spots you don't see that could be above the coolant boiling point, but it doesn't boil because of the pressure. I don't know what to think of that. Any insights on this?
 
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  • #2
The cooling system needs to be sealed, for the obvious reason.

When the water gets hot, the water vapor creates an additional pressure in the air space in the header tank. In fact water will boil when the vapor pressure is the same as the air pressure (about 14 to 15 psi at sea level).

So, the system don't "need to be" pressurized for some reason. Rather, it is impossible fora sealed system NOT to pressurize itself when it heats up.

If the system ran at 190F with no boiling but was not pressurized, it would lose water by evaporation. In other words "steam" would be coming from it, just like if you heated up a pan of water on a stove but kept it below boiling point.

IF the system is working properly, there should not be any local boiling from hot spots, because the water circulation should be fast enough to prevent that. Of course if the system is blocked up by corrosion and other gunk, local boiling may occur.

Local boiling sometimes occurs after the engine is switched off, because the water pump is not circulating the coolant but there is still heat in the engine block. Modern cars have electric fans to cool the radiator and help the water circulate by convection, to stop this from happening.

In a car, it would not be cost effective to make a very high pressure cooling system that could run way above 212F without the water boiling, because it would need a stronger and heavier radiator, more complicated clips for the cooling hoses, etc. Radiator caps are usually designed to "blow" at about 14 psi, whch allows the water to reach about 190F. On the other hand, water cooled nuclear reactors may be designed to run at very high pressures, with no boiling at temperatures up to about 2000F.
 

FAQ: Why does a cooling system need to be pressurized?

1. Why is pressurization necessary for a cooling system?

Pressurization is necessary for a cooling system because it helps to increase the boiling point of the coolant. This means that the coolant can absorb more heat before it starts to boil and evaporate. Without pressurization, the boiling point of the coolant would be significantly lower, and the cooling system would not be able to efficiently regulate the engine's temperature.

2. How does pressurization prevent overheating?

Pressurization prevents overheating by creating a higher boiling point for the coolant, as mentioned before. This means that the coolant can absorb more heat from the engine before it starts to boil and evaporate. Additionally, pressurization helps to maintain a steady flow of coolant through the system, preventing any air pockets or blockages that could cause overheating.

3. Does pressurization affect the performance of the cooling system?

Yes, pressurization does affect the performance of the cooling system. Without the proper amount of pressure, the cooling system would not be able to function efficiently. If the system is not pressurized enough, the coolant would boil at a lower temperature, causing the engine to overheat more easily. On the other hand, if the pressure is too high, it can cause damage to the cooling system components and lead to leaks.

4. Can a cooling system function without pressurization?

Technically, a cooling system can function without pressurization, but it would not be as effective. The boiling point of the coolant would be significantly lower, and the system would not be able to regulate the engine's temperature as efficiently. Additionally, without pressurization, the system would be more prone to air pockets and blockages, which could lead to overheating.

5. How is pressurization achieved in a cooling system?

Pressurization is achieved through the use of a pressure cap, which is typically located on the radiator. The pressure cap has a spring-loaded valve that opens when the pressure in the system exceeds a certain level. This allows excess pressure to escape, maintaining a safe and consistent pressure within the system. The pressure cap also acts as a seal to prevent any air from entering the system, helping to maintain the pressurization.

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