Oil in air cleaner? - JeepForum.com
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post #1 of 11 Old 06-13-2005, 08:10 PM Thread Starter
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Oil in air cleaner?

I have noticed oil in my air box, 2.5 1994 yj, does any body know why? Also backfireing thru the throttle body? thanks in advance...

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post #2 of 11 Old 06-13-2005, 08:12 PM
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I believe it's 'Blowby'. Blowby is created by, someone correct me if I'm wrong, too much oil pressure.
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post #3 of 11 Old 06-13-2005, 08:24 PM
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"blowby" is caused by compression gasses getting past the piston rings and pressurizing the crankcase... basically, worn out cylinders/rings.

Could be a stuck PCV valve if this engine has one, used to have a 4.0L in a Cherokee that would do this all the time, drove it to 180,000 miles and never had an engine failure...
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post #4 of 11 Old 06-13-2005, 08:43 PM
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snowman, you are exactly right... if it's the 4.2 then welcome to your new life, if not then you can fix it fairly easily by replacing what snowman said

not the brightest, but hey, it's more fun this way...

my jeeps not dirty, that's just natural paint.

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post #5 of 11 Old 06-14-2005, 10:10 AM
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Mine had this problem all the time (4.2L) and my filter would be soaked in oil after a couple weeks. Now I just take the hose coming from the top of the crankcase, and direct it towards the ground. No more oil in my breather, but maby not the most environementally friendly fix...
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post #6 of 11 Old 06-14-2005, 10:38 AM
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it's a 2.5L
I had this problem and the valvecover was crudded up with yuch.
Icleaned (blew out) the hose lines and poured a little bit of Sea Foam in the hole the lines goes in. Now more problem. Also the Sea foam got rid of a lot of carbon build-up that came out with the next oil change. Also got me to pass emissions tests in Ohio.

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post #7 of 11 Old 06-14-2005, 10:43 AM
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I had the same problem with my 4.2. It lasted maybe a year or so doing that but the rings were toast!
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post #8 of 11 Old 06-14-2005, 01:23 PM
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Originally Posted by Wood Butcher
I believe it's 'Blowby'. Blowby is created by, someone correct me if I'm wrong, too much oil pressure.
Actually, wrong .. it's crankcase pressure ..

Originally Posted by sasquatch3805
snowman, you are exactly right... if it's the 4.2 then welcome to your new life, if not then you can fix it fairly easily by replacing what snowman said
Not exactly .. it can be sticky compression rings or sticky oil control rings, could also be worn valve guides.
All engines (even new ones) will suffer from ring blowby to some extent .. that's why engines use some form of PCV or CCV vent system.
Basically, an engine crankcase needs fresh air in and contaminated/exhaust air sucked out .. if this system fails somewhere due to clogged/broken/leaky pipes on the "sucking side" the "clean air in side" will be venting oily air into the airbox.
I would check the pipes .. check the PCV valve and elbows and seals for leaks (for CCV there is no valve) .. check the dipstick is firmly in place (yes air will be drawn in here .. look for a rusty dipstick). Is the valve cover leaking ??
If all is well with the PCV/CCV system then check the cylinder compressions .. this will show if it's leaking back into the crankcase. If they are within limits (and also fairly even across the set) I would doubt anything is wrong here .. but if you have a low one that could be your problem.

So ....
I would make sure the fumes are being sucked back into the inlet manifold.

Check the engine oil .. incorrect or dirty oil will cause the piston rings to stick up. Is it really black .. (sign of carbon getting past rings) .. change it a few times and see if it makes a difference.

Check compressions .. this will show if the engine has compression problems .. either a broken (or sticking) ring, or a scored cylinder, or it's just plain worn out.

For what it's worth .. mine was fuming really badly, leaking out the valve cover. I fixed the PCV stuff and now it's fine . ..

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post #9 of 11 Old 06-14-2005, 05:36 PM
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Do a search in forums there are a ton of writeups on this problem and diffrent solutions. I pulled valve cover, repalced valve cover gasket,CCV and PCV valve and slowed it down quite a bit on my Jeep.I also run the hose against firewall and stuffed double the cotton filters in there and it helped quite a bit. No oil leaking all over firewall anymore.

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post #10 of 11 Old 06-14-2005, 07:16 PM
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Crankcase Ventilation

You probably don't have a PCV valve on your model. You probably have a clog in the vacuum between the valve cover and the manifold. This is quite common. If the line is clogged or restricted your engine blow by (normal) will have no place to go except out into the air box. Mine was clogged at the manifold (poked the clog out with a screwdriver then blasted it clean with carb cleaner). Check all the components to make sure you have a decent vacuum pulling the blow by out of the valve cover and into the manifold. If you don't which vacuum line I'm talking about, there are 2 coming from the valve cover. One goes to the air box. The other is for valve cover ventilation. Pull it off the valve cover plug and see if it has good suction. If it does, check the plug itself and clean it with carb cleaner if it has a clog.

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post #11 of 11 Old 06-15-2005, 01:32 PM
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This may seem stoopid...but why does the hose have to go back to the air box? If it's clean it can go anywhere right? If it's dirty (oily) air and/ or the hose is clogged, then it emptys into the airbox which gets the filter oily. Is it just for the environment, or is there a mechanical reason? In other words, can you just put a small piece of hose off the elbow and direct it down and plug/cover the inlet hole on the air box with no decrease in engine performance?

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