I've got a 1990 F-150 with 302 with 140000 miles. It runs great, quiet, no misses, 15-16 on the highway.
But oil keeps collecting in the bottom of the plastic air filter housing. It is no doubt coming up the crankcase ventilation tube that comes out of the side of the oil filler cap. I changed the filter on the end of it, inside the air filter housing, but there is still oil coming up there.The new crankcase filter, which is about 3 inches long, is soaked with oil. From the inside of the air filter housing the oil drips down onto the inside driver's side fender.
I also replaced the PCV valve, which is on the other valve cover.

What's up with this? I sure hope this is nothing serious. Does anyone else have this problem?

 

It is a common problem in older trucks. Make sure after you changed your PCV valve, that the little hose it sits in is not gummed close. It needs to be open all the way. If you made sure that it is way open, you might want to ckeck you compression. If your crankcase pressure gets so high that the PCV system can't handle it anymore, it's usually due to excessive blow by. The pressure then goes out through the second opening, the breather.
Check out this thread for more info:
https://www.ford-trucks.com/dcforum/DCForumID39/3578.html

 

Thanks for the great info and the very helpful thread.

I'll sure check out that PCV valve tube today.

I assumed that the air box's job was to suck fumes out of the crankcase, but it sounds from one of the comments like the opposite is supposed to occur-The crankcase ventilation tube is supposed to suck air INTO the valve cover due to the PCV value pulling air out the other side?

Is this correct? In a healthy normal engine, does air get sucked into or out of the crankcase ventilation tube?

 

It is correct that in a healthy engine you should have airflow from the breather in the airbox through the crankase to the upper intake manifold. This should prevent pressure from building up anywhere in the crankcase and possibly blowing out any gaskets/seals.

 

The PCV valve is working fine, good suction. It looks like I just have a case of a tired 140000 mile engine with too much blow by for the PCV to handle, so it is going up the breather tube into the air cleaner.

Not a good day for my Ford.

 

I'd suggest a compression check!

 

OK, I'll get to the compression test this weekend and post the results here. A friend thought that was the way to go also--after all, the catalytic converter could be clogged and that would cause the problem. The compression test should shed some light.

Thanks.

 

OK,I did the compression test.

1 130
2 140
3 140
4 140
5 142
6 150
7 140
8 140

That seems good for an engine with 140000 on it. The engine runs fine.
I do not know what the compression is supposed to be for a sctock 1990 EFI 302. Does anyone know?

But these numbers look ok--so what is causing the oil to be pushed up into the air cleaner area? Maybe it is too much back pressure in the exhaust system from a clogged catalytic converter?

Any other thoughts out ther before I have the cat replaced? I hate to just replace parts on a trial and error basis.

 

The compression looks good to me. I remember now that I noticed oil in the airbox when I bought my truck. I have since changed a few things on it and never seen oil there again. I did a lot of things, among others, I got a new cat. There's a way of checking your cat: an exhaust shop usually has a temperature-gun (or whatever they call it). It can measure the temperature before and after your cat to see if it flows freely. Other than that? Maybe a blown head gasket?? There's not much left

 

Thanks for the help. I'll have the catalytic converter and exhaust system checked out. There must be too much back pressure. The engine runs fine, just the oil in the air filter area, so I don't think it's a head gasket.

 

Well, I had the exhaust system checked out. They drilled a hole an d inserted an instrument that discovered 1 lb of pressure. The muffler guy said that was too much.

Is this true?

He said the cataltytic converters were clogged. There are two,in the same line.(single exhaust). His solution is to eliminate the two old ones, put one bigger one one, and then run 3 inch pipe all the way out the rear a low restriction muffler. Cost $500.00.

Does this sound reasonable?

 

I've seen hi flow cats for $100-125 bucks.I just paid $85 bucks for a new flowmaster installed.So this guy is gonna charge you $300 bucks to cut off the cats and run one exhaust pipe out the back?That seems high to me.I'd get another estimate.I'm not sure I'd run 3" exhaust pipe,might lose too much back pressure and that can hurt low end power.

Billy

 

definately don't lose your dual cat setup, get two new ones, and have them exchanged. You'd lose a bunch of midrange power if you did that. Cats are cheap, 2 way converters are no more than $65 a peice, and I'd find a different shop to do this, a good shop should charge less than $100 to do the swap. Whatever you do, don't lose the beauty of the true dual system, it sounds and performs so much better. IF you did, even with the single 3" back pipe, that would give you much more back pressure than even dual 2" pipes with a crossover. I'm going to go back and get the numbers, but I just did the math.

 

ok Tom, with 2" dual pipes and an H pipe, or some equalizer, it is 4.5 times less backpressure than a single 3" pipe. Having that little backpressure will not harm you at all, as long as you aren't running open headers for a long period of time. What it will do is dramatically increase your midrange and top end, so don't lose the duals, just have them replaced.
John F. Daly III
The TorqueKing