The thing about fluid loss, is that it has to go somewhere.
If there is no outward leak, then it has to be leaking
internally. If the could be that it draws coolant into the
combustion chamber, and then it vaporizes. If you have white
smoke coming from the exhaust, then that is steam from the
coolant. Also, you may notice water coming from the
exhaust. That is the steam after it has condensed in the cool
exhaust.
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