B757 FLT CREW DEPARTING LAX EXPERIENCED LOSS OF ONE COMPLETE HYD SYS. RETURNED TO LAX AND LANDED SAFELY. FLT CREW DID NOT DECLARE EMER OR PLAN FOR EMER CONTINGENCIES.

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AFTER WE TAXIED OUT; GOT A L ENG HYD PUMP OVERHEAT LIGHT ON. CONTACTED MAINT CTLR AFTER TURNING OFF THE PUMPS. HE INSTRUCTED US TO TURN OFF PUMPS AND THEN TURN THEM BACK ON AFTER COOLING AND CHK HYD TEMP AND PRESSURE. THE OVERHEAT LIGHT CAME BACK ON BUT THE HYD TEMP AND PRESSURE WERE EQUAL ACROSS THE BOARD. HE FELT IT WAS A SENSOR PROB AND NOT A PUMP PROB; SO HE OK'D TO CONTINUE. AFTER TKOF GOT THE STABILIZER TRIM LIGHT ON. WE FOLLOWED THE CHKLIST. THE TRIM SEEMED TO OPERATE NORMALLY. ALL HYD QUANTITIES WERE NORMAL. THIS LIGHT STAYED ON WHEN THE AUTOPLT WAS ENGAGED. APCHING DINTY; WE GOT L HYD SYS PRESSURE LIGHT AND REVERSER LIGHT ON. CHKED L HYD QUANTITY WAS 0.03 PSI. WE GOT THE RUDDER RATIO LIGHT ALSO. NO PTU XFER LIGHT OR HMG WAS ON EICAS. WE CALLED DISPATCH AND HE PATCHED INTO MAINT CTL. THEY TOLD US WE WERE OK TO CONTINUE INTO ETOPS AIRSPACE. AT XA29Z GOT A CALL FROM DISPATCH THAT THE MAINT CTLR WANTED A RETURN TO LAX DUE TO SUPPLIES AND MAINT NOT AVAILABLE AT DEST. WE GOT CLRNC TO RETURN TO LAX AT N3201 PT 2 W12850 PT 7. FOLLOWING CHKLIST FOR L HYD SYS PRESSURE WE KNEW THERE MIGHT BE A PROB WITH NORMAL GEAR AND FLAP EXTENSION. WE LOWERED THE GEAR OUTSIDE OF VTU AND GOT THE PTU XFER UNIT MESSAGE AND THE GEAR DISAGREE LIGHT ON. THE CAPT TOOK OVER CTL OF THE FLT AND WE RAN THE CHKLISTS FOR GEAR DISAGREE AND TRAILING EDGE FLAPS DISAGREE. WHEN WE REALIZED THERE MAY BE NO NOSEWHEEL STEERING WE CALLED MAINT AND HAD THEM MEET US AT TXWY OFF RWY 25R. WE DID NOT DECLARE AN EMER OR ISSUE A CABIN ADVISORY. THE DOA CALLED AN AMBER ALERT AND THE EQUIP MET THE FLT. WE LANDED SLIGHTLY OVERWT AT 205000 LBS VERSUS 198000 LBS. WE MADE A SMOOTH LNDG WITH MINIMAL SINK RATE. WE WERE TOWED TO THE GATE AFTER CLRING THE RWY.