CDR valves, do they need replacement?

[RT]

Hello,
I have heard that CDR valves go bad and when they do they allow excess oil into the intake tract. I just assumed that I have some blowby since the old girl has 221K but now I am just wondering if the CDR is not working as it should? I have oil dripping out of the compressor housing. Maybe turbo seals but this is second turbo. This isn't enough oil to make a fuss about but you know how just a little oil makes a big mess..... TIA, RT

[Hubert]

I think the CDR is just for venting crankcase cases back to be combusted. It won't solve or influence blow by it just vents.

I think the test is to take off the oil fill cap and see if its a vaccum or positive pressure. Should be a slight vaccum. Hold a piece of plastic (heavy Saran wrap or ziplock bag) loosely over top but air tight while running see if it blows out or sucks in. Not too small a piece and don't let it fall or suck into engine.

I don't know if thats for only F engines or S too?

If pressure then CDR is plugged or stuck and maybe blowing oil in when pressure builds???. Some report cleaning it will bandaid it for a while. A little oily residue in intake runner is normal.

[ 09-02-2005, 09:00 AM: Message edited by: Hubert ]

[curmudge1]

Yeah, I think they need to be replaced. I believe there was a thread on this 2-3 years ago or so, you can search for CDR of course.

I replaced my a couple of years ago, and as I recall, it made a difference re oil mess.

HTH, let us know if you do replace yours & whether you think it makes a difference.

[JohnC]

The purpose of the CDR is to prevent too much vacuum from being applied to the crankcase. When it fails, too much vacuum pulls air and dirt past the crankshaft seals and sucks excess oil into the intake. If it plugs (unlikely) then blow-by will pressurize the crankcase and it'll leak all over. If you have excessive blowby, that can also result in excess oil in the intake.

[BobND]

The CDR is WIDE OPEN at all times,(simply allowing the through flow of combustion products, and oil vapor), except when there is enough restriction on the air filter that the engine's intake suction against the air filter begins to draw a vaccum in the crankcase. Then, the valve will be drawn shut, against spring tension, to limit the engine from drawing a wacuum in it's crankcase, and sucking in dirt by it's seals and gaskets, and trying to suck in and burn it's own oil.

Think of it as a "safety valve" that just sits there and does nothing, until there is an intake restriction

I have replaced a couple over the years that developed an EXTERNAL oil leak.

If you look inside, you will see a disc on a diaphragm, held back away from the unit's inlet port, by a spring. This is the position it remains in, unless there is an extreme intake air restriction (unlike a "gasser's" PVC valve that modulates it's position continuously, based on manifold vacuum, which is a product of a gas engine's load, speed, and throttle position).

Replace it, or clean it, if you like, but IMHO, it will have VERY LITTLE, if any, effect on oil consumption.

The reason for the oil in the CDR is that the engine has excessive blow-by, and the oil droplets are finding their way into the CDR, and on into the intake, carried with the extreme flow of combustion products from the excess blow-by.

The older engines, 1982 to 1986, (or thereabouts) attempted to eliminate some of the oil droplets from the crankcase ventilation stream by venting the crankcase from in front of the spinning injection pump gear.

The later 6.2's and the 6.5's simply vent the crankcase through the RH valve cover, which has a wad of steel mesh in it to remove some of the oil droplets from the ventilation stream. It doesn't work real well.

Someone posted on here a while back about a product called the Spiracle, made by Donoldson Air Filter. It is a VERY EFFECTIVE crankcase ventilation oil separator filter that coalesces the oil out of the vapor stream, and returns it to the crankcase.

It's a small glass-fiber reinforced plastic housing with a replaceable filter cartridge in it.

I did some research on the 'net about it, thinking about trying one on my 1994 6.5, but they are ridiculous $$$$ for what little there is to them. (Unless someone knows of a more reasonable source.)

[JohnC]

Originally posted by BobND:
The CDR is WIDE OPEN at all times... except when there is enough restriction on the air filter that the engine's intake suction against the air filter begins to draw a vaccum in the crankcase.While this is conceptually correct, it really doesn't express what's happening. It's not the filter restriction (under normal circumstances) that creates the vacuum, it's the acceleration of the airflow in the convergent duct formed by the elbow between the filter box and the turbo inlet. This will create a vacuum even when the engine is just idling and in the absense of any air filter at all. The CDR is designed to limit that vacuum to a couple of inches of H2O which is a small fraction of the vacuum available. Hence, the CDR spends most of its running life partially closed. If the diaphragm fails, the engine will have way to much vacuum in the crankcase under most circumstances.

[ 09-02-2005, 12:59 PM: Message edited by: JohnC ]

[Turbo Al]

When my CDR failed it would suck one quart of oil from the engine and a cloud would follow me around. Funny thing is that it was worse just after changing the oil -- I have replaced three (two under warrenty) in 170,000 miles.
Al

[BobND]

If the diaphragm fails, they will ooze diesel oil EXTERNALLY, through a little vent hole in the crimped-on cover.