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Dave Nova
Dave Nova, Chevrolet Technician
Category: Chevy
Satisfied Customers: 19452
Experience:  ASE Master Certification. GM World Class Certification
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2002 chevy: the oil fill cap..duramax diesel..crankcase

Resolved Question:

What is the reason there is so much pressure coming from the oil fill cap on my 2002 chevy duramax diesel and so much crankcase pressure
Submitted: 6 years ago.
Category: Chevy
Expert:  Dave Nova replied 6 years ago.

Hello and welcome to justanswer. My name is XXXXX XXXXX I can help you with this problem.


I believe you have a problem with the oil separator at the engine.This should separate the oil from crankcase vapors.I am sending some info to help.Check the hoses carefully. If you find no restricted hoses, the problem will then likely be a stuck pcv valve. Check the valves in both valve covers.



Crankcase Ventilation System Inspection/Diagnosis



DEFINITION: During normal operation the crankcase gases can be seen exiting from the hose at the oil separator.

The maximum crankcase pressure is 4 kPa or 16 in of water at 3,100 RPM measured at the oil level indicator tube.

Oil leak - external

Plugged or kinked crankcase ventilation system hoses
Damaged or loose crankcase ventilation system hoses
Valve rocker arm diaphragm covers loose
Oil separator oil drain hose damaged or loose
Too much crankcase pressure


Normal situation


Cracked hoses


Crankcase Ventilation System Description

The crankcase ventilation system on the 6600 Duramax engine vents the crankcase gases to the atmosphere. Located in both valve rocker arm covers are diaphragms to control the venting of the crankcase gases. As the pressure of the crankcase gases increase they overcome the spring holding the diaphragm in the close position. If a vacuum situation arises in the crankcase the diaphragm closes the port in the valve rocker arm cover. Closing the port will prevent unfiltered air to enter the crankcase.

The crankcase gases travel from the valve rocker arm covers through hoses to the crankcase ventilation system oil separator. The oil separator, separates the oil mist in the crankcase gases. A hose is attached from the bottom of the separator to the crankcase. The oil is returned through the hose to the crankcase.

After the oil mist is separated the crankcase gases are released to the atmosphere through the hose connected to the separator.

No routine maintenance is required to the crankcase ventilation system.

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Expert:  Dave Nova replied 6 years ago.

Here is the location of the valve in the valve cover. There is a valve in both valve covers.