PCV Valve Buyer’s Guide
- The positive crankcase ventilation (PCV) system regulates blowby emissions. It relies on the PCV valve to gather blowby gases from the crankcase.
- This spring-loaded valve contains a tapered pintle that can slide up or down. The sliding pintle can adjust the opening of the valve by changing its position inside the valve housing.
- The PCV valve sucks air and blowby gases out of the crankcase and transports them to the intake manifold. It also removes moisture from the crankcase, extending engine oil lifespan and preventing the formation of sludge.
- PCV valves generally count as maintenance items. Check your valve roughly every 50,000 miles.
- Some of the most familiar issues with the PCV valve include restricted or clogged valves; broken sliding pintles and springs sticking the valve in an open or close position; and damaged PCV hoses.
- Bad PCV valve symptoms include engine oil leaks; engines running lean or rich; rough idling, hard starts, and lean misfires; sludge-related engine damage; and higher emission levels.
- A PCV valve can cost anywhere between $10 and $150. It is sold individually, as part of a PCV repair kit, or as an assembly. Its price tag depends on its brand.
- Take care in selecting the right valve for your vehicle. Even if two valves share the same diameter and hose fittings, their pintle valves and springs may deliver very different airflow performances.
Your vehicle relies on several systems to keep its emission levels within legal limits. One such system is the positive crankcase ventilation (PCV) system. This emission control system regulates blowby emissions, collects fuel vapor from the crankcase, and transports the unburned fuel to the intake manifold.
The PCV system relies on a part called the positive crankcase ventilation valve to gather blowby emissions. If this valve wears out or breaks down, blowby emissions will escape the piston and move into the crankcase. Replace an old or worn PCV valve as soon as possible.
What Is a PCV Valve?
This spring-loaded valve contains a tapered pintle that can slide up or down. The sliding pintle can adjust the opening of the valve by changing its position inside the valve housing.
Depending on the vehicle model and engine, a hose connects the PCV valve to a vacuum port on either the carburetor, intake manifold, or throttle body. These three components connect to the engine and supply the latter with air and fuel.
You can usually find the PCV valve in either a valve cover or the intake valley. Baffles in the cover allow blowby vapors to enter the valve while keeping oil droplets in the crankcase.
What Does a PCV Valve Do?
The PCV system targets blowby emissions, gases that seep through the piston rings and escape into the crankcase. Blowby gases account for roughly 20 percent of a vehicle’s total emissions. As the engine’s piston rings and cylinders get increasingly worn out over the years, the blowby rate increases.
To remove blowby gases from the crankcase, the PCV system pulls air through the breather inlet in the air cleaning housing. The airflow carries blowby gases out of the crankcase and into the PCV valve.
The airflow also removes moisture from the crankcase. By keeping the crankcase dry, the PCV valve extends the lifespan of the engine oil. Getting rid of moisture also prevents acids and sludge from forming in the crankcase. These substances can damage the engine, so the PCV valve extends the engine’s lifespan as well.
The PCV valve controls the airflow from the crankcase to the vacuum port. By moving its sliding pintle down the housing, it increases the volume of air. Conversely, moving up shrinks the opening and reduces the volume of air entering the valve. When the engine runs at higher levels, the PCV valve compensates for the increased blowby gases by increasing airflow.
An operational PCV valve affects the fuel-air mixture in the engine like a vacuum leak in the intake manifold. Your car’s carburetor or fuel injection system compensates for the changing flow of air and blowby gases.
When Should You Replace the PCV Valve?
PCV valves generally count as maintenance items. Check your valve roughly every 50,000 miles and replace it when it shows signs of wear or when you notice symptoms associated with bad valves.
Starting in 2002, many vehicle models with the OBD-II system kept track of the PCV system’s performance. If the flow rate changes because of a bad PCV valve, the powertrain control system (PCM) will switch on the Check Engine Light and log a trouble code.
Earlier OBD-I and OBD-II systems do not monitor the PCV system. However, they check for emission-related issues and will set a trouble code if the bad PCV valve affects the engine’s performance.
Common Problems With the PCV Valve
While PCV valves have long service lives, they can develop problems that reduce their effectiveness. The sliding pintle and spring can break, leaving the valve stuck in just one position. Poor maintenance of the crankcase can also affect the PCV valve.
Some of the most familiar issues with the PCV valve include:
- The PCV valve gets clogged by oil varnish and sludge buildup in the crankcase
- The sliding pintle breaks gets stuck in an open or closed position
- The spring breaks, leaving the pintle stuck open
- Cracked, loose, or leaky PCV hose
Bad PCV Valve Symptoms
The PCV valve is the most crucial part of the PCV system. A problem with the valve will affect the entire emission control system. Bad PCV valve symptoms include:
- Engine oil leaks because of backup pressure forcing the oil through gaskets and seals
- The engine runs lean because the PCV valve got stuck in an open position or a problem with the PCV hose
- Rough idling, hard starts, and lean misfires caused by a lean-running engine
- The engine runs rich due to a loss of airflow from a clogged or broken PCV valve stuck in a closed position
- Engine damage caused by acids and sludge in the crankcase
- Higher emission levels that could lead to failing emission testing
- In OBD-II-equipped vehicles built during 2002 or later, the check engine light illuminates and the PCM logs the associated trouble code
- Pre-2002 OBD-I and OBD-II vehicles will log a trouble code regarding a vacuum leak in the intake manifold
How Much Does a Replacement PCV Valve Cost?
A PCV valve can cost anywhere between $10 and $150. It is sold individually, as part of a PCV repair kit, or as an assembly. Its price tag depends on its brand.
Selecting the Best PCV Valve
While many PCV valves cost relatively little to replace, take care in selecting the right valve for your vehicle. Manufacturers design their valves to deliver an engine-specific flow rate. Even if two valves share the same diameter and hose fittings, their pintle valves and springs may deliver very different airflow performances.
Installing the wrong PCV valve will affect your engine’s performance. A valve that allows too much air to enter the intake manifold will cause a lean fuel-air mixture and associated problems.
Meanwhile, a PCV valve with too little airflow will produce a rich fuel-air mixture. It will also leave more moisture in the crankcase, making it more likely for acids and sludges to build up.
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