Quote:
Originally Posted by stevesnj
And yes a bad cap would allow the water in the coolant to vaporize but there would also bee higher coolant temps because of a pressure reduction.
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High pressure maintained by a properly sealed system allows the coolant to reach higher temperature without simmering/boiling in the hot spots. The temperature variation is not a function of pressure.
What does change when the cap has a pinhole leak is the temperature at which the coolant begins to simmer. Those little bubbles travel to the high points in the system, one of which is the leaky radiator cap so "bloop bloop," while you're driving the bubbles invisibly escape right through the coolant reservoir. Then, when the engine cools down, the remaining internal bubbles, which are pure water vapor, condense and the entire space is taken up by liquid from the reservoir.
The boiling rate is a function of the heat input and the flow rate of the leak.