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oil in the breather box?


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I removed the breather box this evening to have a go at the intake manifold bolts (didn't even get close), which led me to interesting discovery.

 

Oil is getting into the breather box somehow.

 

I couldn't tell for sure if it's all coming in through the, uh, fat line or the skinny lines that plug into the back of the box.

Maybe both.

On the inside of the box that spongey material that covers the skinny line inlets is pretty gooped up with oil, but there's evidence of it coming in through the fat line inlet just below as well.

Or maybe it's coming in through one and out the other. 

143360378_20220512_181323-Copy.jpg.d6f987e4faad871ab6f3576f1c3f83e2.jpg

 

It's certainly made a mess in the bottom of the box, keeping that bolt nice and lubricated I guess.

Looks like a previous owner parked near a mesquite tree.

860089244_20220512_181520-Copy.jpg.3ffe300fcb4183f6399f75a3bba314f6.jpg

 

And the filter is pretty well soaked.

Holding it up to the sun...

1469588500_20220512_181420-Copy.jpg.6f1c9c21ffe99e1be47c7aea76a24a40.jpg

 

Rich deposits of oil infused dirt and gunk on the bottom where it's soaked through.

 

521688335_20220512_181433-Copy.jpg.6eb23d7c8cd490ff5d2f750a2c5fc96c.jpg

 

I cleaned the box up best I could before reassembly and banged the filter against the side of the trash can to get the solid gunk off of there but a new one is in order.

 

I had noticed faint traces of oil at the beginning of the air inlet connected to the box, but the throttle body itself didn't appear to be coated.  I worry that some of this is evaporating when the box gets hot, and going into the intake though.

 

It looks like a new filter is in order so first question, what's the best air intake filter to get? 

 

The one that's in it seems rather high quality in nature.  Good material, looks like it's even covered with a metal mesh, but the media seems pretty well choked up with oil.

It might be a clean and reuse job, I've heard they exist but I've never messed with them.

 

Second question, what is this all this oil in the breather box a sign of?  

PCV issue?

If not that I bet it involves some other acronym I'll have to look up.

 

Or is this just another creative way the old 4.0 uses oil?

 

 

 

 

 

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CRUISER’S VALVE COVER MOD

Most early and even later Renix 4.0s could be bothered by excessive oil in the air cleaner box.

A fix from my old days as Service Manager at a Jeep dealership follows. Information was provided to me from a buddy at JeepTech during those days. I don’t believe it ever came out in a Technical Service Bulletin.

Remove the valve cover and turn it over. Next, remove the fluted tubes that are now facing you by removing three screws on each.

Valve cover flute

Chop 1 inch off each of them. Then, drill a half inch hole as shown in the photo. The flat side of the flute that’s closest to the edge of the valve cover. valve cover flutes (2)

 

Clean and de-burr/sand all rough edges nicely, clean with solvent, and reinstall. Don’t be concerned about the chintzy gaskets that will probably crumble into oblivion when you remove the fluted tubes. They can go back together without gaskets.

Here’s a handy video from my friend Brendan showing more detail.

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I went through this. Its a common problem. Do the Cruiser tip. Also, get one of the FelPro silicon-rubber gaskets. I had issues with the cork ones. I found that the valve cover seal can also cause this issue. I also installed a '95 valve cover at that time. I like the 93-98 valve cover off the ZJ's though. 

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5 hours ago, 75sv1 said:

I went through this. Its a common problem. Do the Cruiser tip. Also, get one of the FelPro silicon-rubber gaskets. I had issues with the cork ones. I found that the valve cover seal can also cause this issue. I also installed a '95 valve cover at that time. I like the 93-98 valve cover off the ZJ's though. 

Thanks.

And thanks cruiser for the tip.

 

A new valve cover gasket is definitely on my list, and I might as well shorten the flute tubes while I'm at it.

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On 5/13/2022 at 2:02 AM, brucecooner said:

I removed the breather box this evening to have a go at the intake manifold bolts (didn't even get close), which led me to interesting discovery.

 

Oil is getting into the breather box somehow.

 

I couldn't tell for sure if it's all coming in through the, uh, fat line or the skinny lines that plug into the back of the box.

Maybe both.

On the inside of the box that spongey material that covers the skinny line inlets is pretty gooped up with oil, but there's evidence of it coming in through the fat line inlet just below as well.

Or maybe it's coming in through one and out the other. 

143360378_20220512_181323-Copy.jpg.d6f987e4faad871ab6f3576f1c3f83e2.jpg

 

It's certainly made a mess in the bottom of the box, keeping that bolt nice and lubricated I guess.

Looks like a previous owner parked near a mesquite tree.

860089244_20220512_181520-Copy.jpg.3ffe300fcb4183f6399f75a3bba314f6.jpg

 

And the filter is pretty well soaked.

Holding it up to the sun...

1469588500_20220512_181420-Copy.jpg.6f1c9c21ffe99e1be47c7aea76a24a40.jpg

 

Rich deposits of oil infused dirt and gunk on the bottom where it's soaked through.

 

521688335_20220512_181433-Copy.jpg.6eb23d7c8cd490ff5d2f750a2c5fc96c.jpg

 

I cleaned the box up best I could before reassembly and banged the filter against the side of the trash can to get the solid gunk off of there but a new one is in order.

 

I had noticed faint traces of oil at the beginning of the air inlet connected to the box, but the throttle body itself didn't appear to be coated.  I worry that some of this is evaporating when the box gets hot, and going into the intake though.

 

It looks like a new filter is in order so first question, what's the best air intake filter to get? 

 

The one that's in it seems rather high quality in nature.  Good material, looks like it's even covered with a metal mesh, but the media seems pretty well choked up with oil.

It might be a clean and reuse job, I've heard they exist but I've never messed with them.

 

Second question, what is this all this oil in the breather box a sign of?  

PCV issue?

If not that I bet it involves some other acronym I'll have to look up.

 

Or is this just another creative way the old 4.0 uses oil?

 

 

 

 

 

Mesquite tree, huh? Sounds like where I grew up. 

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Just some info on how the crankcase vent system is supposed to function for anyone else using the search function.

There are two lines coming off the valve cover. The one on the back goes to the intake manifold, the front goes to the air intake box. In theory, the higher vacuum inside the manifold will suck gasses out of the crankcase, replacing them with clean air from the air box. 
If the flow is interrupted by damaged or blocked lines, low manifold vacuum, leaking oil fill cap gasket or ccv fittings, or excessive blow by, the crankcase pressure will vent via the path of least resistance, generally pushing crankcase gasses and sometimes oil vapours through to the air box. 
 

In this case it looks to me like it’s a reusable filter that was oiled excessively, which isn’t difficult to do. K&N makes a filter service kit with a cleaner and new oil that you can get at most parts stores, although if you want to go back to a standard filter just to confirm the oiling issue is taken care of, that’s not a bad idea either.

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11 hours ago, gogmorgo said:

Just some info on how the crankcase vent system is supposed to function for anyone else using the search function.

There are two lines coming off the valve cover. The one on the back goes to the intake manifold, the front goes to the air intake box. In theory, the higher vacuum inside the manifold will suck gasses out of the crankcase, replacing them with clean air from the air box. 
If the flow is interrupted by damaged or blocked lines, low manifold vacuum, leaking oil fill cap gasket or ccv fittings, or excessive blow by, the crankcase pressure will vent via the path of least resistance, generally pushing crankcase gasses and sometimes oil vapours through to the air box. 
 

In this case it looks to me like it’s a reusable filter that was oiled excessively, which isn’t difficult to do. K&N makes a filter service kit with a cleaner and new oil that you can get at most parts stores, although if you want to go back to a standard filter just to confirm the oiling issue is taken care of, that’s not a bad idea either.

Thanks for the detailed info gogmorgo. 

I love knowing how subsystems work. There are some useful videos out there showing where all the lines around a 4.0 start and end, but they don't give any context, and I like to know what things do.

I've though of taking images of the engine and trying to build maps of the various lines' endpoints with some sort of attached legend explaining their function. Then another image highlighting the various sensors, another for other bits, etc.  I bet somebody's already made them.

 

Anyway, from your description it sounds like if the manifold line were blocked, it would push air into the breather, so I definitely need to pull the manifold line and check for blockage.

If that's clear, I need to get on that compression check I've been thinking about, maybe the oil's getting pushed into the box by leaky valves.

 

I've heard a paper filter is a little bit better at catching dust than the reusable ones, and living in Arizona we got looooots of dust.

If I can get this figured out I'll probably switch.

 

Thanks again!

 

 

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