Tommy;

what engine is this 2wd or 4x4?

the fans should not be running all the time; but they do come on quite frequently if you are running a standard fan switch; what is the temp gauge on the dash doing?

edit: just noticed your in the US - how hot is it where you live?

the oily film in the header tank is a little weird; especially if you've done a fluid test - has the system ever been flushed - are there any other symptoms?