What was found
APU OIL TEMP CAUTION MESSAGE IN FLIGHT. RAN QRH LANDED AT NEAREST SUITABLE. (FLT 5455 FILED CLOSED)REMOVED AND REPLACED WITH SERVICEABLE THE OIL COOLER ON THE APU IN REFERENCE TO CRJ 200 AMM 49-91-07 OPS CHECKS GOOD NO LEAKS NOTED, REMOVED AND REPLACED WITH NEW THE HIGH OIL TEMP SENSOR ON THE APU IN REFERENCE TO CRJ 200 AMM 49-91-25 OPS CHECKS GOOD NO LEAKS NOTED , REMOVED AND REPLACED WITH NEW THE OIL FILTER ON THE APU IN REFERENCE TO CRJ 200 AMM 49-91-10 NO LEAKS NOTED , CHECKED OIL LEVEL OF THE APU ITS FULL NO CONTAMINATES FOUND IN THE FILTER. RAN APU IN REFENCE TO CRJ200 AMM 49-10-00 FOR 1 HOUR WITH LOAD MAX TEMP OBSERVED WAS 184C.