Abstract: In combination with an internal combustion engine, a device for the purification of lubricating oil. Installed as a bypass between the outlet side of the oil pump and the crankcase, the device refines contaminated oil by boiling off under a suitable temperature range condition, contaminants such as condensed water, diluted fuel, and products resulting from partial decomposition of the oil. The device comprises a closed chamber admitting oil under pressure at the bottom of the chamber. The oil is forced through a maze formed by a stack of circular vanes before exiting near the top of the chamber and being returned to the crankcase. An electrical heating element under control of a thermostat heats the vanes to a temperature necessary to boil off the contaminants. The vaporized contaminants can escape through a vent in the top portion of the chamber.