CARS.COM — The positive crankcase ventilation, or PCV, system was one of the earliest emission-control devices used in vehicles. The PCV system draws leftover combustion gases from the crankcase (the oil pan and bottom of the engine) and routes them back into the engine via the intake manifold, where they're burned in the combustion chambers instead of escaping into the atmosphere via your exhaust system.
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Most positive crankcase ventilation systems have a valve known as the PCV valve. When does the PCV valve need to be replaced? Let's take a closer look.
PCV Valve Replacement
The PCV system is seldom listed as a maintenance item, but an old valve that is no longer functioning like it should can cause performance and emissions problems. A PCV valve that's supposed to regulate the flow of these gases is the heart of most PCV systems (some newer vehicles don't have a PCV valve). The PCV valve routes air and fuel from the crankcase back through the intake manifold to the cylinders rather than allowing them to escape into the atmosphere. If the valve doesn't open and close on schedule, or if any part of the system clogs, the result can be a rough idle, sluggish acceleration or increased oil consumption. Rough idling is commonly caused by bad spark plugs, so problems with the PCV valve are often misdiagnosed. If you have a bad PCV valve, PCV valve replacement could eliminate the problems listed above.
Testing Your PCV Valve
The PCV valve is usually mounted in a grommet on a valve cover, at the end of a hose or tube. One way to check whether a PCV valve is functioning is to remove it from the hose or tube and shake it. If you can hear a metallic rattling noise, it's likely in good working order. If you do not hear anything when you shake the valve, it is likely that it is no longer opening and closing like it should. You may be able to clean out the valve to get it functioning again, or you may need to replace it.
Whether an engine has a PCV valve or not, a hose or tube in the PCV system may become clogged from built-up sludge, or a vacuum hose may leak, so it pays to inspect the entire system, clean it if needed and test the valve for air flow. Hoses may also need to be replaced from time to time.
A clogged hose or PCV system or inoperative valve can increase oil consumption because pressure builds when the vapors in the crankcase aren't allowed to flow into the combustion chambers. That additional pressure can force oil past seals and gaskets. If the valve is stuck in the open position, or there's a leak in the system, that will allow too much air into the engine and throw off the air-fuel mixture, likely triggering the check engine light.
Though it's not listed in the maintenance schedule in most vehicles, the PCV system should be inspected periodically to make sure it's still in good condition, especially if engine performance has deteriorated. Fortunately, this valve is relatively easy to test and replace. Whether you opt to replace the valve yourself or you prefer to hire someone for professional valve replacement, installing a new valve could make your vehicle run much smoother.
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