Oil supply system for machines such as internal combustion engines

An oil supply system for an engine comprising an oil pan to receive oil dripping from the engine, an oil reservoir located at a level above the oil pan, a pump-free ascending line for transferring oil from the oil pan to the oil reservoir by a pneumatic pressure difference, the oil pan communicating with the atmosphere only through the ascending line and the oil reservoir, the ascending line having an aperture in the oil reservoir above the oil level therein and having a cross-section such that oil from the oil pan is delivered through the ascending line into the oil reservoir by increased pressure in the oil pan resulting from admission of gases thereto during operation of the engine, and an oil delivery line rising from the oil pan and having a pump for supplying oil to the engine, the ascending line having an opening arranged always at a level above the oil level in the oil pan to receive gases at elevated pressure and being protected against admission of splashed oil or oil droplets from the engine, the ascending line having at least one aperture for the entry of oil arranged slightly above the normal oil level in the oil pan, and means providing a flow path for transferring oil from the oil reservoir to the oil pan.