ACR MLG FLC NOTICED DURING PREFLT THE NEXT MORNING AFTER AN OVERNIGHT LAYOVER; THAT ONE OF THE ENG EPR GAUGES WAS NOT FOR THE CURRENT MODEL ENGS INSTALLED ON THE ACFT. THEY HAD OPERATED THE ACFT WITH THE IMPROPER GAUGE THE NIGHT BEFORE.

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FLEW AN ACFT WITH AN IMPROPER RAM AIR TEMP/EPR GAUGE INSTALLER. ON MAR/XA/01; I FLEW AN ACFT FROM MKE TO MCI. ACFT IS A JT7 PWRED ACFT. THE PREVIOUS CREW HAD WRITTEN UP THE RAM AIR TEMP/EPR GAUGE; HAD IT REMOVED AND REPLACED; BUT MAINT INSTALLED A GAUGE THAT CORRESPONDS TO THE JT9 ENG. THIS CREW FLEW SEVERAL LEGS AND DID NOT DISCOVER THE PROB. WE RECEIVED THE ACFT ON AN ACFT CHANGE FOR OUR FINAL NIGHT FLT TO MCI. AT NIGHT; IT IS ALMOST IMPOSSIBLE TO TELL WHAT RATING THE RAM AIR TEMP/EPR GAUGE CORRESPONDS TO; IE; -7 OR -9. THE MARKINGS ON THE GAUGE ARE COVERED BY A SWITCH. THE ONLY WAY IS TO KNOW THE GAUGE HAS DIFFERENT RANGE OF SETTINGS FOR A CORRESPONDING TEMP. I DID NOT NOTICE THE DIFFERENCE. THIS PROB WAS DISCOVERED THE NEXT DAY WHEN A CAPT QUESTIONED THE SETTING THE FO HAD SET IN THE EPR GAUGES FOR TKOF. TO CORRECT THIS PROB; MAINT SHOULD XREF THE PART NUMBER IN THE TECHNICAL MANUALS TO ENSURE THE PROPER GAUGE IS INSTALLED IN THE ACFT. IN THE FUTURE; I WILL BE SURE THE PROPER GAUGE IS INSTALLED FOR ALL FLTS BY CHKING THE MARKINGS ON THE GAUGE AND XREFING THE EPR'S ON THE TKOF PWR SETTING (TKOF DATA).