In one of the most recent versions of Weblogic 12c it happens that logs of type .out are not being automatically rotated as they should.
This is evidenced in the Oracle BUG and affects from version 22.214.171.124 onwards:
BUG:27487203 – MANAGED SERVER .OUT FILES DO NOT GET ROTATED UPON RESTART OF MANAGED SERVER
Momentary solution: Enable log rotation at the start of the Server.
Perform the following steps:
Finally we must confirm that the log has actually been rotated.