As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
NR 1 ENGINE OIL FILTER BYPASS LIGHT ILLUMINATED AT CRUISE POWER. LIGHT OUT AT IDLE. RETURNED TO ORD. *S/D* CORRECTED SYSTEM FROM FUEL TO OIL. THE OIL FILTER BYPASS LIGHT ILLUMINATION WAS CAUSED BY COKING. BLOWING OUT THE LP 5 AND LP 6 LINES AND CLEANING THE OIL SCREEN SOLVED THE PROBLEM.