Crankcase Depression Regulator Valve

Fuel Filter Article

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Cdr Valve

From the Manual:

The CDR valve is very similar to a PCV valve on gas engine vehicles. It stands for Crankcase Depression Regulator.  It's purpose is to recycle the exhaust gases that manage to get past the piston rings and into the crankcase.

If you're using a quart of oil every 1K miles you might want to take a look at their CDR valve.

The Crankcase Depression Regulator (CDR) Valve maintains crankcase pressure. Pressure must be regulated to prevent oil consumption through the intake system, and to prevent oil leaks due to excessive buildup of pressure. Control is accomplished by regulating the blow-by gases into the intake system to be reburned. Inside the CDR valve, a spring holds open a valve plate that connects to the CDR valve body with a flexible diaphragm. The valve plate is capable of restricting the outlet passage to the turbocharger air inlet duct when airflow pulls it closed against the force of the spring.

Crankcase pressure at idle . . . . . . . . . . . . . . . . . 0-1 inch H 2 O
Crankcase pressure at 2000 RPM . . . . . . . . . . . 2-5 inch H 2 O

Crankcase Pressure Check
1. Bring the engine to operating temperature.
2. Obtain a water manometer (J23951)
3. Remove the oil dipstick and attach the hose of the water
manometer, to the dipstick tube.
4. Start the engine and observe the manometer at idle:
b" If the reading indicates that the crankcase pressure is 1
inch or H 2 O or less go to step 5.
b" If the reading indicates that crankcase pressure is highest
than 1 inch H 2 O inspect the CDR valve and recheck
crankcase pressure. (if the CDR valve is good check engine
5. Run the engine at 2,000 RPM, observing the manometer.
b" If the reading indicates crankcase pressure is in a negative
state (-4 to -5 inch H 2 O), the system is OK.
b" If the reading indicates crankcase pressure is in a negative
state greater then -5 inches of H 2 O replace the CDR
valve and retest.
b" If the reading indicates crankcase pressure is in a positive
state, review test and results of step 4."

Actually, you can make a water manometer easily. Get a few feet of some clear plastic tubing. Mount it to a board so you have a 'U' about 1.5 feet high on each side and about 3" wide. Fill it about 1/3 with water and mark the water level. Hook one side up to whatever you are testing and measure how many inches of water the level has changed.

AMG part number is 5714132 and it costs around $84
GM#25097699 Crankcase depression regulator valve $44.98
ACDelco# CV910

The CDR valve is responsible for controlling the pressure/vacuum in the engine crankcase, and separating the oil mist from the air and returning the oil to the crankcase. When the pressure builds up because the CDR is stuck closed the crankcase pressure will increase, and could force oil past some gaskets and seals that could result in leakage.

If the CDR is stuck open oil mist from the crankcase will be sucked into the engine and burned as fuel, however, it is heavier and thicker than diesel fuel and, having greater BTU output, causes excessive heat in the cylinder. After a period of time, cylinder and head temperatures will reach unacceptably high levels causing the head bolts to stretch and the head gasket to fail.

A quick way to inspect your CDR valve is to remove the air cleaner assembly and look into the air intake with a flashlight. If you see engine oil mist in the intake manifold, test it out per the instruction above or get a new one.