PCV System

Heated PCV valves
  • A few manufacturers add heating elements to their PCV valves.  It is thought cold temperature could cause a non-heated valve to freeze and stick, because of moisture drawn through the system.  By heating the valve, freezing is prevented.



Troubleshooting PCV

  • Failure Symptoms

    • Oil Leakage (stuck closed)
      • A bad PCV valve can cause excessive oil leakage and consumption. A PCV valve helps relieve pressure in the crankcase. If the PCV valve malfunctions, crankcase pressures can increase, forcing oil through seals and gaskets.
    • Air Filter Contamination (stuck open)
      • A buildup of pressure in the crankcase due to a faulty PCV valve also pushes water vapor through the breather element. A breather element is a filter used to trap excess oil from the crankcase system. This water vapor, mixed with combustion gases, leaves hydrocarbon and oil deposits on the air filter, which may result in greater fuel consumption and the need to clean or replace the air filter.
    • Decreased Engine Performance (stuck open)
      • Lean condition that causes misfire. PCV valve will usually cause a poor or unstable idle due to it causing an excessive vacuum leak.
    • Increased Emissions and Fuel Consumption
  • Testing

    • Check for oil in the PCV hose (stuck open).
    • Check  for oil sludge on the dipstick (stuck closed).
    • You can remove the PCV valve and blow through it to check its operation. If you can blow through it in both directions, the valve is stuck open.
    • Dipstick Test.
      • Take out a dipstick and check for crankcase vacuum with engine running.
      • Leaking PCV valve will produce extra vacuum in the crankcase, usually more than 0.5 – 1.5 psi (1 – 3’’ Hg). Block the PCV hose to see a difference in crankcase vacuum.
      • If vacuum is not present, check if unmetered air is sucked in by the crankcase by blocking the PCV hose and watching fuel trims. If fuel trims normalized, the air leak is in the crankcase.
        • Don’t forget to smoke test around main seals under vehicle.
    • Smoke Test.
      • PCV with vent might leak, which can be normal, depending on the design.
      • If smoke pressure doesn’t build up, try to block PCV hose.
        • If pressure starts to build up, you might have a leak in the crankcase which is hard to see from the top.
        • Block the PCV hose and let crankcase build up pressure with engine running. At the same time, check for oil leaks, e.g. check main seal, between transmission and engine.
  • Remedy

    • Try squirting a few shots of brake cleaner through the valve to clean it up inside. More often than not, you can simply free up the valve and return it to normal operation. I’ve rarely come across a valve that can’t be cleaned up.
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