1
general::
Phrase(s): blow off (some) steam
Go to let off (some) steam.
McGrawhill's American Idioms And Phrasal Verbs
2
general::
Also, let off steam. Air or relieve one's pent-up feelings by loud talk or vigorous activity. For example, Joan's shouting did not mean she was angry at you; she was just blowing off steam, or After spending the day on very exacting work, Tom blew off steam by going for a long run. This metaphoric term refers to easing the pressure in a steam engine. [Early 1800s]
American Heritage Idioms