or draft) that pulls gases out of the crankcase. To prevent too much vacuum being created, the blow-by gases are replaced by fresh air using a device called a breather. The breather is often located in the oil cap. Many breathers had a cup or scoop and were located in the air stream of the engine radiator fan. This type of system is called "Pressure-Suction" type and air is forced into the scoop of the breather and by vacuum is draw out by the road draft tube. Another type used of the pressure suction type was used on VW Porsche air cooled engines whereby the front crankcase pulley has a reverse screw built into it which brings air into the engine and air escapes the crankcase with the road draft tube. This system works very well in getting rid of crankcase vapors which are harmful to the engine. As per the earlier engines, the road draught tube system also created pollution and objectionable odors. The draught tube could become clogged with snow or ice, in which case crankcase pressure would build and cause oil leaks and gasket failure. On slow-moving delivery vehicles and boats, there was often no suitable air slipstream for the road draught tube. In these situations, the engines used positive pressure at the breather tube to push blow-by gases from the crankcase. Therefore, the breather air intake was often located in the airflow behind the engine's cooling fan. The crankcase gases exited to the atmosphere via a draught tube. Positive crankcase ventilation (PCV) History Although the modern purpose of a positive crankcase ventilation (PCV) system is to reduce air pollution, the original purpose was to allow an engine to operate underwater without the water leaking in. The first PCV systems were built during World War II, to allow tank engines to operate during deep fording operations, where the normal draught tube ventilator would have allowed water to enter the crankcase and destroy the engine. In the early 1950s, Professor Arie Jan Haagen-Smit established that pollution from automobile engines was a major cause of the smog crisis being experienced in Los Angeles, California. The California Motor Vehicle Pollution Control Board (a precursor to the California Air Resources Board) was established in 1960 and began researching how to prevent blow-by gases from being released directly into the atmosphere. The PCV system was designed to re-circulate the gases into the