500 mls of Roundhouse steam oil, ISO Viscosity 220. The current oil supplied by Roundhouse was chosen after consultation with the oil's manufacturer and discussion as to its precise application and working environment. To deliver the correct amount of this 220 weight oil, the feed hole in the lubricator of modern Roundhouse locos has been reduced in size as the now thinner oil picks up and flows far more freely. Using thicker 460 oil in the current models should not be a problem as far as lubrication is concerned (slightly less getting to the cylinders), but may lead to long term carbonisation in the superheater. Using the current 220 oil in an older Roundhouse loco that was originally supplied with the thicker oil will not cause any problems other than an oily engine.