What was found
AFTER ENGINE START UP, A FAINT ODOR OF OIL FUMES WAS NOTICED IN THE COCKPIT. DURING TAXI, THE ODOR CONTINUED, BUT WAS ATTRIBUTED TO THE PROXIMITY OF OTHER JETS. THE APU WAS RUNNING THROUGHOUT THE STARTUP, TAXI AND TAKEOFF. IMMEDIATELY AFTER T/O, THE OIL ODOR WAS VERY STRONG. WE ELECTED TO LEVEL OFF AT 23000' AND CALL COMPANY. O2 WAS USED AND FLIGHT TERMINATED. THE APU WAS NOT USED DURING LANDING. POST FLIGHT INSPECTION REVEALED NOTHING OUT OF THE ORDINARY WITH ENGINES OR APU. AFTER AIRCRAFT HAD SIT FOR ABOUT AN HOUR WE DID NOT NOTICE ANY SMELL WHEN WE FIRST ENTERED AIRCRAFT. WE PERFORMED ENGINE RUNS AND PRESSURIZED AIRCRAFT WITH ENGINES AND APU AND DID NOT NOTICE ANY UNUSUAL ODOR. REPLACED WATER SEPARATOR SOCK WITH NEW. RAN AIRCRAFT AGAIN AND PRESSURIZED TO MAX DIFF WITH NO DEFECTS NOTED. ALL WORK IAW MM CH 21-10-95, 21-30-00.