ON TWO SEPARATE B757-200 TYPE ACFT; AFTER ENGINE LOW PRESSURE FUEL FILTERS WERE CHANGED; ENGINES EGT TEMP SPIKED; EXCEEDED LIMITS; ENGINES CHANGED.

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ON ACFT X; AFTER THE ENG LOW PRESSURE FUEL FILTERS WERE CHANGED; AND SUBSEQUENTLY DURING THE LEAK CHK THE R ENG EGT JUMPED AND ROSE RAPIDLY EXCEEDING 570 LIMIT CAUSING ENG DAMAGE AND REPLACEMENT. 26 DAYS LATER; ACFT Y AFTER ENG LOW PRESSURE FUEL FILTERS WERE CHANGED; DURING LEAK CHK THE R EGT EXCEEDED 701. ENG WAS RUN BY THE FLT CREW DUE TO PAX ON BOARD. CREW RPTED EGT JUMPED AND ROSE RAPIDLY. NOTE: I DIDN'T RUN EITHER OF THESE ENGS BUT PREVIOUS WEEK I RAN AN ENG FOR SOMEONE ELSE AND NOTICED AN EXTREME JUMP IN EGT AFTER FUEL FILTER REPLACEMENT. COULDN'T FIND WHICH B757 IN WEB MAINT HISTORY. UNKNOWN. SUSPECT ENG NEEDS TO BE WET MOTORED TO STABILIZE ENG FUEL SYS BEFORE ENG RUN WITH IGNITION. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR STATED ALL OF HIS COMPANY'S B757 ACFT FUEL TANKS ARE BEING TREATED WITH BIO-CIDE. ENGINE LOW PRESSURE FUEL FILTERS ARE ROUTINELY REPLACED AFTER CERTAIN NUMBER OF FLIGHT HOURS BECAUSE OF THE BIO-CIDE BUILD-UP IN THE FILTERS. DUE TO THE UNEXPECTED EGT SPIKES INCURRED WHILE ACCOMPLISHING ENG RUN FUEL LEAK CHECKS AND SUBSEQUENT ENGINE CHANGES; HIS COMPANY ENGINEERING DECIDED TO INCORPORATE HIS SUGGESTION TO WET MOTOR THE ENGINES WITH FUEL PUMPS ON; IGNITION OFF; BEFORE PERFORMING THE NORMAL ENG RUN WITH IGNITION ON. SO FAR; THIS PROCEDURE SEEMS TO HAVE ELIMINATED THE EGT SPIKES AFTER THE FILTER CHANGES.