When a new boiler is installed, there is going to be an ongoing process of getting the oil out of the boiler. This is going to go on for awhile. Rest assured, that it will at some point be over and the boiler will run quiet. The oil is 'in' the cast iron and the pipes that are used are pretty much bathed in oil as threads are made on them. Its as if the steam has to steam clean the oil out of the pores of the metal. This oil will then float up to the surface and when enough is there, totally mess up the boil. This messed up boil will show itself in several ways. You may only have one symptom show up or you may have all symptoms show up. One never knows how it will present itself. In this video link is a steam boiler that when the oil returns makes hammering noises from inside the boiler. You could also see a wicked up and down movement in the gauge glass, or a sudden drop off of the ability of the boiler to get steam to the radiators. Any or all of these symptoms indicate oil on the surface of the boilers water.