Oil getting into air filter question.

[1996XJ]

My wife had a similar problem with her 2015 JKU so I went through the steps of replacing the PCV valve and then checking all of the other usual suspects with no change. Took it in to the local dealer and a brand new tech figure it out. The insulation mat on the hood! Under hard acceleration, the insulation would get sucked down and obstruct the air inlet for the airbox. That was creating so much vacuum in the intake system that it was pulling oil through the PCV valve. A pair of scissors, 10 minutes and the problem was solved.

Thanks when I get it back I'll double check this is not the cause.

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[1996XJ]

Now I see why dealer services get such a bad reputation... they called me today to say they only replaced the breather tube after they told me the pcv valve would be changed when I talked to them last. The tonneau cover was also being replaced as it ripped in half. I was told the cover arrived two days ago... long story short the cover arrives at the very end of this month, and they would like to inspect the tube again at that time. So basically I just need to wait for it to leak again and go through all the rental car shenanigans again at that time. The only honest thing they said was there is a tsb relating to engine noise and possibly the oil leak could be related to that. But since there is no noise they changed the tube lol.

 

[Maximus Gladius]

Do you have blow-by? Several replies here have mentioned it but I haven’t seen yet if you actually have it. (I may have missed where it might have been said)

Turn on engine and pull the oil fill cap. Is there air blowing out of the fill hole?

Some of us have blow by while others do not. Blow by is intake air getting past the rings causing pressure in the crankcase which then flows out the PCV. If you have air blowing out the fill hole, the compression in the rings isn’t as high as they should be. @ShadowsPapa might have a different opinion here but I don’t think I’m too far off the mark. If you have no air blowing out, your compression is great and no need to check. My engine does not have blow by and shouldn’t be considered “normal”. I personally think something isn’t quite right.

What oil are you running? I’ve also learned from a great trusted source of mine that type and quality of oils used with better additive packages make a world of difference when it comes to eliminating blow by or PCV leak.

 

[MMMojave]

Get a catch can. Should solve the problem.

 

[ShadowsPapa]

Some of us have blow by while others do not. Blow by is intake air getting past the rings causing pressure in the crankcase which then flows out the PCV. If you have air blowing out the fill hole, the compression in the rings isn’t as high as they should be. @ShadowsPapa might have a different opinion here but I don’t think I’m too far off the mark. If you have no air blowing out, your compression is great and no need to check.

Blow-by is the result of improperly sealing rings letting combustion gases and pressure past the piston. That includes wear, broken rings and so on, even a gouge in the cylinder wall.

One test is the crankcase vacuum test - pull the oil fill cap, adapt a vacuum gauge to the oil fill tube or hole, depending on the engine.
You should have vacuum. You should be able to put your hand over the hole with the engine running and feel the vacuum.
If there's no vacuum or even pressure, you have excessive blow-by. I say "excessive" as no rings can seal absolutely perfectly and some combustion pressures/gases will always get through past the piston rings. The PCV is supposed to evacuate that and pull a vacuum.
The vacuum actually helps seal the rings by increasing the pressure differences between the top and bottom surfaces of the rings, pressure on the top gets behind the ring and helps push the rings outward in some ring designs.

I found detonation destruction in my 390 when I pulled the oil fill cap off, got in and started the engine and watched really subtle "puff puff puff" out the oil fill tube.
In other cases, an engine I worked on literally had oil pooled in the bottom of the air filter housing. I found low compression, pulled the engine, pulled the head, flipped it around on my engine stand, removed the pan, removed a rod cap and the piston dropped to the floor! There was no tension on the rings at all. Each piston literally fell out as I pulled rod caps.

 

[ShadowsPapa]

Get a catch can. Should solve the problem.

Bandaid masking real issues. Hack/duct tape instead of repair...

But where he's seeing the oil - it's not likely to help oil in that place. It will prevent oil into the intake, but not where it's coming out of into the air tube. That's where the crankcase gets fresh, clean air - it's not going to resolve the problems.

 

[1996XJ]

Do you have blow-by? Several replies here have mentioned it but I haven’t seen yet if you actually have it. (I may have missed where it might have been said)

Turn on engine and pull the oil fill cap. Is there air blowing out of the fill hole?

Some of us have blow by while others do not. Blow by is intake air getting past the rings causing pressure in the crankcase which then flows out the PCV. If you have air blowing out the fill hole, the compression in the rings isn’t as high as they should be. @ShadowsPapa might have a different opinion here but I don’t think I’m too far off the mark. If you have no air blowing out, your compression is great and no need to check. My engine does not have blow by and shouldn’t be considered “normal”. I personally think something isn’t quite right.

What oil are you running? I’ve also learned from a great trusted source of mine that type and quality of oils used with better additive packages make a world of difference when it comes to eliminating blow by or PCV leak.

I get the truck back tomorrow, i can check some of the stuff members mentioned here. The oil is what the dealer puts in for me, I am hoping they use quality oil and correct amounts but some people have had issues with simple dealer oil changes. According to them they have checked the PCV system and it's functioning as it should. I sincerely doubt they went beyond that. They are waiting for the problem to return so I can bring it back in I suspect. I'll keep you all posted incase this being resolved helps a member in the future.

 

[Hootbro]

They claim the pcv valve is on the back of the tube?

The PCV valve is on the backside of the passenger side valve cover. It is somewhat tight space between the valve cover and the firewall. One can remove it by hand reaching back with a blind feel and pull up the lock tab and quarter turn it and pull back toward firewall to remove.

 

[cmcveay]

On the JK 3.6, the PCV valve is on the back side of the passenger side head, very close to the firewall. Although it is a PITA to get to, the actual work wasn't too bad, just took a small ratcheting wrench with a torx tip.

 

[ShadowsPapa]

On the JK 3.6, the PCV valve is on the back side of the passenger side head, very close to the firewall. Although it is a PITA to get to, the actual work wasn't too bad, just took a small ratcheting wrench with a torx tip.

The JK has nothing to do with this - it's the pre-upgrade engine and quite different in PCV.
These are PUG engines, 2nd gen, the PCV is twist-lock in the back, no wrench needed.

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