However sometimes there are leaks allowing the water / steam to escape.
If a gasket is blown - to the oil sump or released via the spring loaded filler cap / pressure release valve because of excessive pressure in the water system caused by "pumping" during the compression stroke .
A pipe may also perish or burst or leak at the joints.
The water pump could also be the culprit .
Get into the habit of checking the water (and fluid) level.
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Never do today what you can put of until tomorrow - Student motto