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CDR for dummies

mezc

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bakersfield,ca
So I read some threads about this PVC or CDR valve and still is not clear, I took it out and oil came out from inside (10 mml), I blew in the inlet and there isn't any restriction, zero differential pressure. Seems to me that any exhaust from the oil cap will go in to the air intake.

So, is this good or bad? :drool:
 

OL AG '89

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Kingwood, Texas
CDR defined "borrowed from flashoffroad.com"

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.

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.

Get the rest of the story at Crankcase Depression Regulator Valve

Not sure about the pressures as listed, but my guess is anything close is good...

So I guess as long as the spring on the inside still has a decent "spring" to it you could just wash out "carefully" and reinstall....
 

Tanner

Active member
1,013
11
38
Location
Raleigh, NC
There's info here as well regarding the 'Tuna Can' - CDR\PCV - what’s it all about, Alfalfa? - Diesel Place

Some guys wash it out w/ soap & water, others with gasoline; my understanding is that it has a rubber or synthetic diaphragm inside...

NAPA p/n: '2-9445' - or maybe listed as 'CRB 29445' - titled as 'PCV valve' or description states 'Depression Regulator Valve' - NAPA Online shows price at $45.49 each

GM p/n: 25098706 - my understanding is that it is NLA at dealers. (someone care to chime in here?)

'Tanner'
 

lavarok

Well-known member
1,119
33
48
Location
Fellsmere, FL
The GM part numbers for the CUCV are:

12340256 / 25042443 / 25042462 / CV871

There are civilian model replacements that may or may not fit properly. I have not tried any of the civilian model replacements so cannot confirm or endorse their use. I've change many cdr valves and always use the mil-spec part.

Some civilian model replacements are:

CV870 / 25042248 / 25041698
 

Tanner

Active member
1,013
11
38
Location
Raleigh, NC
Agreed Ian that there will possibly be some variation in the civvy vs mil-spec CDR -

depends on what a previous mechanic/owner/hacker has done to said vehicle.

'Tanner'
 

AJMBLAZER

New member
2,688
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Location
Paducah, KY
I have been told just clean and strain it out and put it back in..Don't waste the your money on replacing it..all it is a mesh filter.
WRONG.
There's info here as well regarding the 'Tuna Can' - CDR\PCV - what’s it all about, Alfalfa? - Diesel Place

Some guys wash it out w/ soap & water, others with gasoline; my understanding is that it has a rubber or synthetic diaphragm inside...

NAPA p/n: '2-9445' - or maybe listed as 'CRB 29445' - titled as 'PCV valve' or description states 'Depression Regulator Valve' - NAPA Online shows price at $45.49 each

GM p/n: 25098706 - my understanding is that it is NLA at dealers. (someone care to chime in here?)

'Tanner'
Some dealers can get them if they check the dealer system and look outside their area if no one locally has them. A few guys got them that way as little as a year ago.

I bought one of those NAPA parts a few years ago and it was far smaller and the inlet/outlet tubes were the wrong size. Maybe I got the wrong one but it definitely wasn't a bolt on.
The GM part numbers for the CUCV are:

12340256 / 25042443 / 25042462 / CV871

There are civilian model replacements that may or may not fit properly. I have not tried any of the civilian model replacements so cannot confirm or endorse their use. I've change many cdr valves and always use the mil-spec part.

Some civilian model replacements are:

CV870 / 25042248 / 25041698
I've got a civilian 6.2L CDR on Big Ugly and a milspec CUCV CDR on The Blazer. Just sorta ended up that way. Configurations are overall similar. I had to shorten The Blazer's hose from the manifold a bit but it was originally a C-code motor and not a J-code anyway.
 
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