I have a 1996 F250 4x4 over 8500 GVWR with 85,000 miles, and I am getting crankcase oil in my air filter. My air filter is soaked and it's getting so bad that it's starting to drip out of the box. It is coming from the crankcase vent tube that runs from the oil fill on the valve cover to the air filter box. I have lost power and fuel mileage (expected). I just removed the well-used spark plugs, compression tested the cylinders, and got 125 lbs/in2 on all 8 cylinders.
Two questions:
1. What is good compression for this engine?
2. Any ideas about the cause of the oil in the air filter?
Any help would be appreciated.

 

Generally, oil getting into the air cleaner is signs of excessive crankcase pressure. This could mean something as bad as excessive blow-by of the rings or oil returns holes not allowing the oil to return to the pan and filling the valve covers with oil or maybe a bad pcv valve.

I would first check the pcv valve and see if it is working. With the pcv valve out of the valve cover, remove the oil filler cap and see how much blow by is excaping the valve cover. Next, check the valve seals to see if they have cracked and pieces have stopped up the oil drain back holes in the heads.

 

Thanks for your reply.
I have checked the PCV valve and it's OK. I have run the engine with the oil fill cap off and I didn't feel any blow-by. I know that's not scientific, but you can usually tell a bad engine that way. I'm getting 125 psi compression per cyl, but I don't know if that's good or bad.
Could this have anythins to do wit it: My catylatic converter has been gutted, but it still has a tube (EGR?) attached which runs to the smog pump. Could exaust gas be returning back into the crankcas and causing this? I might try to block this off first before removing the valve covers.