Effects on Engine Overheating and Pressure Dynamics

[tommd]

TL;DR

will the temperature rise if the pressure is restricted

I tried posting this earlier, but being my first time somehow got it in mechanical and I wanted it in thermodynamics so I am reposting here. Sorry for the confusion:

Automotive cooling system

Not sure if this is an appropriate forum for this question or not, but I will try.

Many current automotive cooling systems have a system that is completely filled with coolant and no room for air or expansion, other than slight bulging of the hoses, etc. A pressure cap, typically 14 psi is on the radiator. As soon as the system starts to warm up, the coolant expands and pressure increases. When the pressure exceeds the radiator cap setting, the coolant is pushed out of the closed system and into an overflow tank. When the system cools down, the coolant is drawn back into the radiator.

I have a report of a system that, due to a service issue, ended up being completely sealed. No room for expansion of the coolant and NO pressure cap or pressure relief of any type. As the engine warmed up, we suspect the pressure went very high as there was nowhere for the expanding coolant to go, although we have no reading of the pressure. Although the operator had no way of knowing the increase in pressure, he did notice the temperature gauge went high into the “red” zone. The engine was shut down before the pressure increased to the point of breaking a hose, radiator, or some other item due to the high pressure.

My question- I recognize with no pressure relief cap, the system would have been damaged due to extreme pressure. But why did the temperature rise? It seems that although under higher than normal pressure, the coolant would have still been flowing throughout as normal, picking up heat from the engine and transferring the heat to the radiator where it would have been cooled. I assume the pressure would not have exceeded 100-200 psi, as the hoses or radiator would have probably blown by then. Would this type of pressure somehow have affected the coolant in a way it could not transfer the heat? Why did the temperature rise?

Under normal conditions, a pressure cap is used to increase the system pressure to raise the boiling point of the coolant. To my understanding, that is all it does. I thought it does not affect the cooling process itself. But now I am wondering, does pressure affect cooling in other ways? In this case, it may have increased the boiling point very much, but it also caused the engine temperature to go up drastically. If not a coolant issue, maybe the pressure affects the thermostat operation?

Thanks,

Tom

 

[Juanda]

I tried posting this earlier, but being my first time somehow got it in mechanical and I wanted it in thermodynamics so I am reposting here. Sorry for the confusion:

You're referring to this I believe.
Auto cooling system question

That thread already got some traction and good answers. I don't think there's a need to have it duplicated.

 

[tommd]

I do not know why it got posted in the other area. The responses there, although good,seem to be more oriented towards the mechanics of the cooling system, where I have little questions. My question is if this amount of pressure can affect the cooling of the water. I understand there is localized boiling in a cooling system- nucleate boiling??? Could that be affected by the pressure? As I stated above, increased pressure should only increase boiling temperature, not cooling ability???
Thanks,
Tom

 

[Juanda]

I really don't know where to answer your questions. Having two threads feels confusing.
Since the other thread seems to be becoming the main one, I'll answer there.

 

[Doc Al]

Mentors note: @tommd, Please do not create multiple threads on the same question. (If something seriously needs to be moved, report it and Mentors will consider the request.)