Why pressure in coolant system?

[frankbauer@thevine.net]

mike sez:
>Can someone tell me why coolant systems are made to develop & maintain
>pressure in them?

water boils at 212dF.
add some coolant and the boiling temp rises.
put the mixture under pressure and it rises further.
it is cleaner and more efficient to operate the engine when coolant
temps are in the 230dF range, so they use tricks to get the coolant mix
to operate at the higher temps without boiling over.
(also, the heat transfer is practically nonexistent wherever boiling
occurs since the liquid phase isn't touching the hot metal.)

frank

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