YACT: What would make oil get into the air filter?

[BooGiMaN]

My freind's 90 jeep cherokee, is getting oil in the air filter. What would cause this?
I had no idea what to tell him but now im curious to know myself.

 

[jemcam]

Blow by, meaning the rings aren't sealing good, which causes pressure in the crankcase, where it gets sucked into the breather.

It could also be the PCV valve, I'm not that familiar with that car. Some cars also have a filter in the air cleaner housing coming from the valve cover to the air cleaner. That little filter could be missing or need replacing.

 

[radioouman]

PCV may be bad, and he's sucking air out of the top of his valve cover into the air intake.

Or, he lost his oil filler cap, and oil is spraying everywhere when he drives, and oil is being pulled into the air intake. Just guesses

 

[Vic]

Bad PCV valve. OR... in some older cars (don't know about '90 Cherokee), the ventilator for the PCV is inside the air filter near the throttle body, so a really dirty air filter could cause the engine to suck air from the ventilator, pulling oil up from the sump (yes, I have seen it, on an old 240Z).