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How much crankcase pressure should there be ?

A

Acesneights1

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If I disconnect the CDR at Idle I can feel the crankcase build a decent amount of pressure. Is that normal ? I have alot of oil by the turbo inlet. I'm wondering if it's bad CDR or blowby. Should there be pressure without CRD hooked up ? I tried the same thing on the CUCV and I know that engine is tight as a bull's ass durin fly season and it did the same thing. Too bad GMCTD isn't around. I may have to build me a manometer.
 
Take an air compressor for example since a diesel is a big compressor with fuel. My air compressors all build crankcase pressure. My small Wayne compressor actually has a little rotating valve that lets the pressure out of the crankcase but not the oil.

The way i figure the pistons moving up and down will create crankcase pressure, The bottoms of the pistons will move air around just like the tops will. I've never held my hand over the oil fill without the CDR hooked up, but i'm sure both of mine will do the same thing.
 
The difference would be that there is nowhere for air to enter the bottom of the piston, its all a wash when one piston goes up another is going down. That is except for all the air and fuel that blows past the rings. On the other side intake air is sucked in by the vacuum of the piston moving down or pushed in by turbo. Even at idle I have a lot of pressure out the oil fill tube. Thats why there is a CDR or draft tube, etc...to allow pressure to vent. The CDR doesnt really do anything at idle but allow it to vent, the slight vacuum of intake helps a little. when turbo kicks in there is so much vaccum that the CDR progressively closes as vaccuum increases. This way it prevents too much vacuum from sucking your oil out. If CDR is stuck open the crankcase will have too negative of pressure under boost and would suck oil out and could prevent proper lubrication. If CDR is stuck closed it would allow too much positive pressure and blow dipstick out.

Having it well vented should be adequate for proper operation and prevent oil seal leaks, but the intake vacuum allows you to burn them fumes. #1 emissions output of our engine most likely.
 
If the dipstick is blowing out, or you are losing a bunch of oil. You can run the Heath CDR test, but it doesnt really tell you if the CDR is working, just that its open under no load like it always is. The CDR closes under load/vacuum from turbo progressively up to like 8psi boost, so you cant really test it in park. It could be stuck open and the vacuum created by the engine as you rev it would show you good test. Then under load, sustained boost, you could be sucking oil out. Although I guess we could see how much vacuum there is in park when revving, and then compare with CDR inline with manometer, and if its the same then its not really a total function test.

Of course with the breather I put in the valve cover, my CDR could just be sucking air through the breather into the crank case and into the intake under high boost. And it may not create enough vacuum to close. At warm idle, vapor comes out the valve cover breather even with the CDR on the oil fill.

I dont have something that actually shows a different part number for NA vs turbo CDR, but that is what others have said, that they are different. With my valve cover breather setup Id prefer a CDR that closed at lower vacuum amount on oil fill tube. I suppose any large PCV valve would work. They work the same way, just opposite in operation.

Under high vacuum at idle in a gasser the PCV chokes the flow, and as rpms go up vacuum goes down and opens up valve.
 
There will always be some pressure leaking past the rings.

If the sucker is huffing and blowing then there are issues. The CDR is designed to vent the pressure into the intake.

If everything is in good order the CDR is supposed to maintain a slight negative pressure in the crankcase.

Most high mile 6.2/6.5 engines will see some blowby but the issue is how much.

I have seen many fairly low mile 6.5 TD with really sloppy turbo inlets, due to oil blowover.

MGW
 
Well I used to replace the PCV valves in cars every year when it was only a couple bucks. The CDR is probably something that is a regular maintenance item every 5 years or something like that.
 
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