oil in compressed air

hi. I have kaeser CS91 screw air compressor,I have oil in pipe,we changed filter separator but after about 1 week we finded oil again.when we checked filter separator again, i finded oil in it.the oil type is ok and temp of oil is about 80degree Celcious. please help me also I want to know my compressor work continuosley and unloaded time is less but temp of oil is 80degre Celicious.is there any problem for this condition? thanks, vahid, iran