I have a '93 F150 302 5.0 EFI that I recently got back on the road after being parked for about five years. When I got it back out to be my daily driver i replaced transmission, torque converter, all front end bushings, plugs, wires, cap and rotor, and changed the oil.

After the first thirty miles of driving I noticed a small amount of smoke coming from the left side of the hood so I stopped and found oil leaking from the air box. Initially I blamed it on an incorrect (non vented) oil cap that I had put on because mine went missing, so I got the correct cap on it and didn't notice new oil in the air box for about 150-200 miles. Now i'm about half a quart low on oil and there is cloudy aerated oil at the bottom of the air box again. It is coming out of the return hose that comes from the oil filler neck to the airbox.

Can anyone help me out with what might be causing this?

 

Blow by............... (Pressure in crankcase)

Start by replacing the PCV valve, (rear of passenger side valve cover) and making sure the vacuum line going to it is not plugged up..

 

First thought is a bad PCV located on the passenger side valve cover, under the intake plenum. Once you verify it is good or replace it (Motorcraft only please) then you may need to do a compression check/leak down test if the problem persists.

The crankcase is getting pressurized by either a plugged PCV or excessive blow-by from the piston rings.

 

I type slower than you...

 

Not really.. I just got there first!!!!!

But, you said it better...

 

+1 on PCV or piston rings.

Had the same blow-by problem earlier this year. Piston rings were shot. Was cheaper to have the engine replaced than replacing the piston rings.

 

When you pull the PCV valve, make sure you have strong vacuum there (check that with the engine running). I have seen a few Windsors where the vac port on the back of the intake plenum that the PCV hooks up to is plugged up with carbon.

 

Replaced PCV valve and blew out the vacuum hose connected to it (which was not plugged up) and am still having the same problem. Any other ideas?

 

Your piston rings are shot, you'll either need to completely disassemble your engine, or replace with a new/used.

I opted to replace my engine with a used w/ only 60,000 on it when my piston rings went out earlier this year.

 

If it's still throwing out oil after the PCV replacement, as every poster in here already mentioned your piston rings are shot. You can switch to a cheaper and thicker oil (20w50) and run it like that for a while if it isn't loosing too much oil. As long as you keep the oil level under check you can run the truck undefinitely, but it will only get worse in time, the options to address this are the ones stated by Alex.

 

Before you totally jump on the whole piston ring thingy I would do a compression test to be positive.

 

Well shucks.

 

drive it till it blows up and then go find a new motor. you drive it like that for a long time as long as you check your oil often and keep oil in it

 

You can drive it, but you will eventually have, or maybe already have, a major lack of power. I couldn't believe how much more responsive the replacement 302 in my truck was after swapping out the old engine with bad piston rings. The old engine eventually couldn't even go over 60 mph. It would not budge any higher.

 

Skrappy- you have blow by from the worn rings and will need to eventually replace the rings/ rebuild the engine. However, if you want to put off the ring replacement/rebuild for a while and keep most of the oil out of the airbox/ intake tract, you can either buy or build an air oil separator. google it, there are several sites out there that will tell you how, basically you plumb the separator between the pcv valve and the intake manifold vaccuum source. the separator has filter media in it to capture most of the oil vapors. i did this to my 351 windsor in my 1990 f350, and was able to keep oil out of the intake manifold/ air filter box/ throttle body. just realize that your entire intake tract from the airbox to the intake valve is gonna be coated in oil.