how can my motor be running hot when engine is at lower rpm. . on 1996 Ford F-350

as i accelerate my temp comes down. running hotter then should but never overheats or boils over. replaced waterpump, radiator, tstat. Can this be a partially plugged cat. check engine light comes on then goes off after about 8 seconds. engine seems to never lack power. still runs but i dont want to damage engine. this is my work truck and need it asap

Asked by for the 1996 Ford F-350
Check to make sure fan is operating when engine is warmed up.
fan is running to best of my knowledge after truck is warmed up i open hood and fan is running.
If your check engine light has come on and off get code read and post the result. Could just be temp. sensor has failed which means no potential damage to vechicle. But get read to make sure.
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bad fan clutch,,,
a new fan clutch was installed and nothing changed. i can hear a click in top radiator hose almost like an air pocket or extra pressure pulses through it. exaust system is very old. this problem is a tough one. i may run out of money before i find problem.