On many diesel engines crankcase is kept under a slight vacuum to reduce the emission of harmful substances into the atmosphere and protect oil and engine parts from mixture of vapors. During engine operation exhaust gases through the leaks in the combustion chamber may seep into the crankcase, as well crankcase vapors of oil and water must be removed. To carry out a desired gas extracting process oil separator is installed, on one side it is connected to the crankcase and on the other with a turbocharger inlet. Also, it has a drain whereas collected oil can be led back to crankcase or withdrawed from use. One of the most successful designs belongs to RACOR and very often seen applied on Cummins QSM engines, John Deere and Caterpillar. In addition to the above, the separator has a filter status indicator and a crankcase pressure regulator.