PCV or Positive Crankcase Ventilation is an emission system that has been part of your automobile since the early sixties. It has been quite a forgettable system in that it was typically very reliable and maintenance wise was very inexpensive to look after and repair. As of late this system has increased in complexity. You may have guessed, increased complexity means increased failure rate, and increased expense.
What is PCV and what does it do? The explanation gets back to the very basics. The internal combustion engine (both diesel and gasoline) produces motive power by containing an explosion of air and fuel and using the force of that explosion to twist a shaft. By design it is impossible to contain all the gases from the explosion. The sealing of the piston in the cylinder that connects through a rod to twist the crankshaft is not perfect. Each explosion sneaks some not so clean gases called blowby past the piston.
What to do with these sneaky gases? The other side of the piston is called the crankcase. At 2000 engine revolutions per second your four cylinder engine’s crankcase is absorbing 4000 puffs of blowby per minute. The crankcase is where your engine oil is stored and circulated. If the crankcase is not vented somehow pressure will build up and end up pushing all your oil out past various seals and gaskets.
Early engines simply vented the crankcase out to the atmosphere. If you make the path for these gases circuitous enough they will not be carrying any of the liquids and engine oil out with them.
Since these gases contain air pollutants the late sixties engineers came up with a simple solution to keep them out of our atmosphere. Simply suck them back into the engine and burn them again. At low engine loads these gases are metered through a properly sized orifice into the engine (PCV valve). At higher engine loads the PCV valve closes and all the gases are simply drawn through a hose past a PCV filter and directly into the engine. No metering required. Again these gases were sent circuitously through screens or baffles to remove any engine oil being carried with them.
Fast forward to the 21st century and PCV systems are much more complex especially on turbocharged vehicles. The PCV system is not just about emissions. It never was. Ideally blowby gases will all be evacuated from the crankcase without allowing any of the acids and contaminants they carry to be deposited in the engine or engine oil. Maintaining the correct flow is important for the well being of an engine. Keeping blowby gases out of the engine oil is more important today now that engine oil changes are way less frequent.
Increased complexity has resulted in much more elaborate valve systems and engine oil separation components. There are many more hoses. Simple parts are now part of major components. A failed PCV valve in one vehicle requires a new intake manifold. In another the whole valve cover has to be replaced. Others may have simple parts but poor access and poor materials. Getting to the failed component involves other brittle components which are often broken along the way.
Failed PCV systems will many times turn the check engine light on. Sometimes you will notice poor running. Sometimes you will notice high oil consumption. Sometimes you won’t notice much. Whatever the case, get it fixed. A properly functioning PCV system is necessary for long term trouble free motoring.