Crankcase pressure
04-06-2019, (Subject: Crankcase pressure ) 
Post: #1
Crankcase pressure
I have a 2000 cat c12 with around 680k miles on it. ,there original, it's a day cab and was used locally under a load to were it calls for alot of boost it will leak oil on the ground. Like. It's pushing it past gaskets or seals on the motor. Mainly on the drivers side. But does it all over. I had to put a chain on oil fill cap because it would blow it off. The blow by tube isnt plugged. And when it idles there is hardly any coming out of it.

On a calm day ( no wind) pulling a loaded trailer it uses no oil and doesn't leak. Sometimes a guy can go a cpl weeks without adding oil, but if you get a few days we're it's pretty windy you have to add about a half gal of oil. Because it leaks it out. When it's running or going down road going through gears the exhaust burns clean


The turbo has some black soot, not bad but it's there. The cac side of turbo has some discoloration like soot but it's not bad. Just there. When u take the hoses off and start engine u can smell exhaust coming out of the turbo that goes to the cac. The boost gauge in truck reads normal under a load.

I have a cac tester but need to get an adapter to go on inlet side of turbo so I can test the turbo itself.

When I take the cac hose off the turbo and pressurize the system from there you can hear air leak into the crankcase. So the air is going through the cac to the intake into the cylinders that are open and is somehow getting into the crankcase. When u air system up to 20psi u can fill the air coming out of the oil fill tube hit your hand.

I've had the truck for a year now and it's always done it. Hasn't gotten worse.

Recently it started to have a vibration at idle and under load to were it shakes the steering wheel and the dash. It always ran smooth.

I'm the morning when it's cold from sitting over night it sounds like crap until it gets warmed up.

I am sending a driver today to get a diagnostic computer that I bought. So now I can do a cut out test etc etc.

The truck once it gets warmed up starts super easy, just runs rough.

I realize it could be alot of things, head, ring, piston etc etc. I was thinking maybe it's a bad injector and it has a bad seal or the injector is bad itself to were it pushes air past it in the compression stroke??

Has good oil pressure. Not weak at all and the water temp runs cool. You don't lose oil pressure and water temp doesn't go up under a load.

How can a guy pinpoint what cylinder it is and what it is? Or has anyone had this problem before on a cat?
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04-06-2019, (Subject: Crankcase pressure ) 
Post: #2
RE: Crankcase pressure
you could always pressurize the engine and turn the engine by hand to see if it has higher than normal leak rate into the crank case when certan vales are open or closed? - Also a boroscope to check the liner wear?


User's Signature: ->: What I post is just my own thoughts and Opinions! --- I AM Full Of S__T!.
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 Thanks given by: race7820000 , DSTdriver
04-08-2019, (Subject: Crankcase pressure ) 
Post: #3
RE: Crankcase pressure
I got a cat crank turning tool coming. So I can watch the valves open and close etc. When I pressurerise the intake system it won't hold more than 21psi. I did a cut out test and it says they pass. When I hit cylinder 2 it barely changes the tone of motor. Number 5 is maybe a little worse but not much

Cyl 1,3,4,6 all sounded the same, like they were actually cut out.

I attached a Pic


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04-08-2019, (Subject: Crankcase pressure ) 
Post: #4
RE: Crankcase pressure
you said when you start it you can smell exhaust coming out of the charge side of the turbo. sooooo i would assume turbo seals are kablewy and soon the turbo and when your running on a non windy day your not building a bunch of exhaust or boost pressure but when its windy you are...so when your building boost/exhaust pressures might these gases be going through the oil seals and into the crankcase causing your pressurization that is then what makes her puke oil out every orifice she has.

also sounds like maybe some bad piston rings/liners unless its air going past the valve stems into top of head and then into crankcase.

just my thoughts.
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 Thanks given by: race7820000
04-08-2019, (Subject: Crankcase pressure ) 
Post: #5
RE: Crankcase pressure
I agree on the the turbo thing lol but what I don't understand is I unhook the hoses from turbo, then pressurize the cac from the charge side, so basically my air compressor is acting like the turbo.

Now, since I'm doing that I'm only putting air to the intake side, if the intake valve is closed air shouldn't go in the cylinder to begin with so it wouldn't make it to the exhaust.
When you out your ear up to the oil fill and put it to 20 psi, it sounds and feels like a steady stream of air, like if you have a loose fitting on a air gun.

It doesn't burn oil. You never see it burn it.

I pulled the oil fill cap off to try and see if there was a rythem to it like maybe longer cycle I guess you would call it of air hitting my hand.

I could feel any rythem just a light steady flow of air. It had blow by coming out like some one lit a cig and it was burning is how I would describe it.

It starts right up. Like right away and runs. Doesn't have power it use to and I'm assuming because it won't let the boost stay were it needs to lol

I would rebuild it but I want to understand why it's the way it is first.

To me it feels like a dead cylinder and proly is. Cause Cyl 2 shows it passes with the cutout and the injector selnoid passes the test also, but my theory is the reason why it doesn't sound like it makes a difference is because it doesn't have the compression to make a hard boom on on the stroke and that is why the motor feels like it barely changes tone etc
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04-08-2019, (Subject: Crankcase pressure ) 
Post: #6
RE: Crankcase pressure
Also I capped the air compressor line that goes to the intake when I aired up the system.
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04-08-2019, (Subject: Crankcase pressure ) 
Post: #7
RE: Crankcase pressure
i might also look into valve stem seals letting air by and into crankcase if its not making alot of blowby at idle to account for the pressure causing the oil leaks. theres Rings, Air Compressor, valve stem seals, head gasket blown only to an oil passage, turbo seals thats the only places i can think of that can allow pressure into the system without introducing incorrect fluids, i believe CATs use a similiar cam driven fuel injector to cummins 870/871 on some of their engines just have a big bulky center with i believe electrical connections if they are HUEY injectors like what was used in powerstroke 7.3l/6.0/i beleive its a 446 international engine and a few others then i could see compression getting into the oil through the injector but with cam driven style i dont beleive any oil passages are near the injector unless its blowing past all the seals on the injector into the head space.
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04-08-2019, (Subject: Crankcase pressure ) 
Post: #8
RE: Crankcase pressure
Gottcha. If I end up pulling the head, I think a person almost has to rebuild the whole thing since it's right there?

I think this weekend I will take valve covers off one at a time and hopefully find the leak. I wonder if a guy with the valve covers off do each Cyl at a time and use a piece of heater hose and your ear and try and listen to were exactly its coming from.? I need to buy a bore scope.

If I rebuild it does a guy get cat oem parts only? Or is there a particular aftermarket brand that is good?
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04-08-2019, (Subject: Crankcase pressure ) 
Post: #9
RE: Crankcase pressure
couldn't a person pull the rockers and actuate the intake valves by hand, measure the static flow rate for each cyl after it pressurizes the chamber with an EVAP machine (or a cheap welding machine flow meter)?.

just a curious thought.


User's Signature: ->: What I post is just my own thoughts and Opinions! --- I AM Full Of S__T!.
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