PCV stands for positive crankcase ventilation. An important parts of the positive crankcase ventilation system is the crankcase breather hose that works to circulate the air around the engine keeping the engine clean and cool. These hoses will often become brittle and crack from the heat or may come apart from the main system when clamps break or separate. Problems caused by this can run the gamut from a failed emissions test to a rough idle. It is important to replace them as soon as possible to ensure that they will not rupture willing driving and possible cause the car to stall and leave you stranded. There are many different crankcase breather hoses on the car and they may require different clamps and tubes to go with them. It also plays an important part in emissions and keeping your car from emitting too many toxic gases that may harm the environment. The positive crankcase ventilation systems were developed in the 1960s for improvements to the emissions systems on cars so cars built before then do not have them.
Breathing is very important to your engine. After combustion takes place there is a slight amount of blow-by (oil and unburnt fuel) in the top of the engine that needs to be dissipated quickly or the engine may erupt due to excess pressure. From the earliest days of the internal combustion engine, one of the great engineering challenges is how to allow this pressure to escape from the engine. Many different designs have come along to solve this challenge and that is what the PCV crankcase breather hose is part of. Improvements in these designs have made vast improvements in emissions reductions as well. The PCV crankcase breather hose itself is usually made of thick rubber and designed to withstand the extreme temperatures that may develop in a car's engine.
The PCV crankcase breather hose can be easy to replace however it is a good plan to consult a qualified mechanic if you want to make sure that the job is done right. Here are some basic instructions to give you an idea of how these parts are supposed to be changed. There may be several on your car so check a service manual if you are going the work yourself.