I have a 01 Honda rancher 350 and iv noticed the fan hasn't came on in about 3-4 months. Any clue on what the problem is ? And is there supposed to be oil in the radiator ?

fan should come on when its hot, rad should have oil , its actually a oil cooler. the oil in the rad would be pumped from engine to be cooled so it might not have oil in it when engine is not running. I would do some checking on why fan isn't coming on.