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Breather Valve / Crankcase Vent Valve

Posted on: 15 April 2013
Credit: Tune-Tech

TuneTech Racing


1994 to Current – They are all pressure controlled crankcase Ventilation systems


What it looks like:

Five different types




Symptoms of failure:

  • Rough Idle
  • Whistling noise from Vent Valve
  • Engine light on – Misfire faults
  • Oil leak from Vent Valve


How it functions:

These valves might all look different but they all function the same. It uses a spring and diaphragm assembly to control the crankcase pressure. Simply put the unit controls the oil/air pressure by maintaining a certain vacuum in the crankcase (bottom end / engine block) during all engine operating conditions.



The breather valve is item no.1. Oil is pressured by the oil pump and cleaned by the oil filter. It is then squirted into the crankshaft and falls to the bottom of the crankcase. Occasionally unburned fuel and exhaust gases also get in and if it remained in the crankcase and condensed, the oil would become diluted and the viscosity would change, decreasing its ability to lubricate. In all modern cars these gases are expelled through a outlet out of the crankcase through the breather valve (crankcase valve) and into the intake manifold. “The clean air prevents a potentially explosive atmosphere within the engine crank case.”



If a breather is aged or clogged-up it results in the seals on the turbo to come off and can cause failure. It should be incorporated into the inspection (major) service to prevent a big expense.

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