[cdowns]

first off i doubt you have oil on the cooling fins of your radiator or heater core !! the fins are on the outside and no liquid circulates thru the fins it circulates thru tubes that the fins are attached to
i suggest you run a 190degree thermo if that doesn't supply heat then you've either got a blocked heater core or a phlenem box that's filled up with debris either of which will require taking out and replase/repairing the heater core