What was found
(CAN) REPEATED CREW REPORTS OF NR 1 OIL TEMP HIGH. CLIMBS TO 100 DEG IN CLIMB AND BACK DOWN TO 98 DEG. NR 2 READS 78 DEG IN CLIMB AND CRUISE. NR 1 FUEL TEMP AT 52 DEG AND NR 2 AT 36 DEG AFTER MAINTENANCE TROUBLESHOOTING THE LH ENGINE OIL COOLER WAS REPLACED IAW AMM TASK 79-21-01-400-801. NO FURTHER FAULTS NOTED. OIL AND FUEL TEMPS NORMAL WHEN STABILIZED AT HIGH POWER. FOUND BYPASS VALVE WEARING INTO VALVE SLEEVE- CAUSING DAMAGE/JAMMING VALVE. DIFFICULT TO REMOVE VALVE SLEEVE-STUCK IN COOLER. OIL COOLER ASSEMBLY REPLACED IAW DHC8-400 AMM TASK 79-21-01-400-801. AIRCRAFT GRND RUN. OIL TEMP AND FUEL TEMP NORMAL. FOUND BYPASS VALVE WEARING INTO VALVE SLEEVE RESULTING IN DAMAGE/JAMMING OF VALVE.