As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
PDX - IN CRUISE FLIGHT, NR 1 ENGINE FUEL TEMP BELOW THE GREEN ARC. FOLLOWED CHECKLIST, WITH NR 1 AUX PUMP ON THE FUEL TEMP WAS DECREASING BY 2 DEGREES WITH POWER REDUCTION. ALL OTHER PARAMETERS NORMAL. MAINTENANCE REPLACED THE FUEL HEATER THERMAL ELEMENT. OPERATIONAL CHECKS GOOD. AIRCRAFT RETURNED TO SERVICE.