A DC8-71 ON CLBOUT AT FL280 DIVERTED DUE TO #4 ENG HIGH EXHAUST GAS TEMP IN OVERTEMP INDICATION. CAUSE UNKNOWN.

Narrative

DEPARTED ZZZ AFTER SEVERAL DELAYS: FIRST DELAY; ACFT LEAKING FUEL AND REQUIRED MAINT. SECOND DELAY; LOADING OF ACFT WITH DISPLACED FREIGHT. ON CLBOUT OUT OF FL280 (CAPT FLYING) I NOTICED EGT ON #4 WAS ABOVE MAX. I POINTED THIS OUT TO THE CAPT AND WE REDUCED PWR TO BRING THE EGT BACK TO BELOW LIMITS. PRIOR TO THIS REDUCTION; I COULD HEAR THE ENG SURGING. WE INFORMED ATC THAT WE WOULD BE RETURNING TO ZZZ AS WE WERE DIRECTED TO DO SO BY COMPANY. WHILE DSNDING; WE NOTED EGT INCREASING AND OIL TEMP INCREASING. I IMPLORED THE CAPT TO SHUT THE ENG DOWN AS TEMPS WOULD ONLY INCREASE AS WE DSNDED. HE FINALLY CAPITULATED AND I INFORMED ATC THAT WE PERFORMED A PRECAUTIONARY SHUTDOWN ON #4. WE DID NOT DECLARE AN EMER AS THIS IS NOT PREDICATED IN OUR TRAINING. WE ALSO HAD NO NEED AS WE HAD NO OTHER PROBS. AN UNEVENTFUL LNDG WAS MADE AT ZZZ. IN A CONVERSATION WITH ANOTHER CAPT HE ASKED ME IF WE TURNED THE PERFORMANCE MONITORING COMPUTER. WE HAD NOT. THIS CAPT TOLD ME THAT ENG SURGING IS SYMPTOMATIC OF PERFORMANCE MONITORING COMPUTER FAILURE. WE WERE AT THAT POINT ABLE TO CONSULT THE ABNORMAL CHKLIST FOR PERFORMANCE MONITORING COMPUTER FAILURE. IT WAS NOT NOTED THAT ENG SURGING WAS SYMPTOM OF PERFORMANCE MONITORING COMPUTER MALFUNCTION. INCLUSION OF THAT WOULD BE HELPFUL.