Abstract: A small portion of oil being circulated by the engine's pump is constantly diverted to a specially-constructed filter where solid contaminant particles are intercepted. The oil still under pressure is then directed to a dehydration chamber wherein its pressure is reduced and it is directed through a heat-exchange pipe and drops onto a horizontal spreader plate pierced by a multiplicity of small apertures distributed over its relatively large area. Spreading of the oil in a thin layer over the plate effects vaporization of liquid contaminants therein. The vapors are drawn off from the top of the chamber by vacuum and dispensed to ambient air or recirculated to the carburetor. Purified oil flows by gravity from the chamber to the crankcase.