As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
APPROX 5 MINUTES INTO DEPARTURE, DURING CLIMBOUT, CREW WAS ALERTED BY AN EICAS MESSAGE "HYD SYS NR 2 OVER TEMP". DECISION WAS MADE TO RETURN TO DEPARTURE. AS THE ACFT DESCENDED, CREW NOTED THE MESSAGE EXTINGUISHED AND THE TEMPS STARTED TO COOL OFF. ACFT MADE AN UNEVENTFUL LANDING AT DEPARTURE. AFTER TROUBLESHOOTING THE HYD SYS NR 2 IT WAS DETERMINED THE HYD SYS NR 2 RESERVOIR WAS DEFECTIVE. THE RESERVOIR WAS REPLACED AND THE ACFT WAS RETURNED TO SERVICE.