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Tech Tip: MINI PCV System Diagnostics And Measurement Of Pressure

All current MINI engines incorporate a pressure–controlled crankcase ventilation system that uses various crankcase ventilation valves, depending on the engine type. Although the valves all look different, they function similarly using a spring and diaphragm assembly to control the crankcase pressure.

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All current MINI engines incorporate a pressure–controlled crankcase ventilation system that uses various crankcase ventilation valves, depending on the engine type. Although the valves all look different, they function similarly using a spring and diaphragm assembly to control the crankcase pressure.

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A properly functioning pressure control valve is designed to maintain a slight vacuum (underpressure) in the crankcase that ensures reliable cross-case venting during all engine-operating conditions. Some of the causes and results of a malfunctioning crankcase ventilation system are listed below.

Causes of Excessive Overpressure (Pressure)

– Internal engine damage or wear.

– Obstruction in the crankcase ventilation system.

– Defective pressure control valve.

Results of Excessive Overpressure

– Damage to the engine oil seals.

– Increased engine oil consumption (can be misdiagnosed as a defective turbocharger).

– Excessive engine oil in the intake system.

– Excessive engine oil in the charged intake tubes or the intercooler on turbocharged engines (can also be misdiagnosed as a defective turbocharger).

– Engine oil dipstick is dislodged from the guide tube (if equipped).

Cause of Excessive Underpressure (Vacuum)

– Defective pressure control valve.

Results of Excessive Underpressure

– Damage to the engine oil seals.

– Increased engine oil consumption.

– Excessive engine oil in the intake system.

– Rough engine idling or engine misfire.

– Whistling or howling noise from the engine (can be misdiagnosed as a defective turbocharger).

– Increased mixture adaptation values.

Measuring The Pressure

The pressure in the crankcase can be measured with a pressure transducer. Pressure readings can be taken at the oil filler cap. MINI recommends taking an oil filler cap and attaching a plumbing fitting with 3/16” barb and 1/8” NPTF opening.

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Specification and actual readings from the vehicle may vary by up to 110%, but not more than 4.0 mBar.

Mini oil cap with barbed fitting.

Pressure Specifications:

 

W10 = 1.0-6.0 mBar

W11 = 2.5-4.0 mBar

N12 = 22 mBar

N14 = 38 mBar

N16 = 36 mBar

N18 = 36 mBar

B36 = 24 mBar

B38 = 24 mBar

B46 = 26 mBar

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