Mystery oil consumption

[cleandan]

I am helping a friend with a 427/454 FE that is consuming HUGE amounts of oil without any of the normal signs of oil consumption.
There is no oil burning out the tail pipes.
There is no appreciable oil leaking, or signs of leaking either, other than fairly normal FE weep.
There is no oil smell when the engine is running and the engine runs very well.
When driving behind the car there is no noticeable anything, smells, sights, sounds, nothing.
The PCV system appears to be working properly and not sucking oil.
By all accounts there should be no oil consumption issues yet the oil loss is on the order of one quart per 100 miles driven.
I recently pulled the cylinder heads and had them reworked by a competent shop. The heads are iron B9 castings with some port work but nothing special. All aspects of the heads were perfect when reinstalled. The engine was tuned and runs with no issues other than oil loss. As a matter of fact the engine runs really great. I am totally lost as to where this oil could be going because none of this makes any sense when checking possible areas of oil consumption or loss.
Fill the crankcase, drive around a few hundred miles, check oil level and find it quarts low with not a sign of why.
Do any of you have possible ideas where the mystery oil loss could be coming from?
Thanks for any and all help.

[chris401]

Any oil in coolant? Had a couple of early 70's 360/390 blocks leak oil to coolant where a rocker arm oil feed in the block cracked.

[Joe-JDC]

Just about put money on the PCV system sucking it out and burning it.  There are different PCV valves with differing flow rates.  Does the system have a mesh strainer/separator installed in the PCV/road draft tube location?  Valley tin installed?  Joe-JDC

[ericwevans]

I have a bad cylinder on the left side that causes my FE to eat oil at about the same rate (1qt/130mi) as you mention, the only noticeable external sign is that I have turn downs on the exhaust under the left turn down the street and parking space at work have a slight darkening.  Try pulling the plugs, my #6 plug told the tale.  I still drive it just fine like that.

[blykins]

Have a bore scope?

If so, you can use it to see where it's coming from.  A scope down a spark plug hole will show oil/excessive carbon on the top of a piston.   Stick it down an intake runner and you can see oil pooling on the top of a valve head or running down a valve stem. 

A little detective work will show where it's coming from. 

Modern ignition systems will burn oil without much problem and can show clean plugs. 

[cleandan]

A few answers to questions asked.
The PCV is plumbed into the oil fill tube on the front passenger side of the intake, about 3/5 the way up on the high side (toward distributor).
There are two baffled plugs in the tube at the bottom. Each plug has a half moon cut that is opened like a louver.
The engine is running the intake valley tin.

I will have him check the coolant for oil contamination.

A bore scope is a great idea, thanks.

This is a long distance diagnosis.He is in Jefferson Indiana and I am in MN.
Thanks for all the helpful input so far.

[nhsohc]

Where is the PCV valve located?  Is it upright or does it have a spring?  Where is the crankcase vented from?  The back of the intake or the valve covers?  With that much oil missing, I would think there would be evidence of oil all around and under the carb, on the floor of the intake manifold.

[WConley]

That unconventional PCV system is the first suspect in my mind.  It's easy enough to disconnect the PCV valve and plug the vacuum hose (or just leave the PCV valve out to suck open air if removing it messes up the carb tune).  Put a hundred miles on it and you'll have a quick answer.

The other possibility is stuck oil rings.  Rislone has worked well for me in those situations.

I'm not suspecting the usual Print-O-Leak intake gaskets because you've had the heads off...

[shady]

I am wondering if this engine used oil right from the start after the build, or did it slowly develope where it has just got to this point, or was it good one day & started gulping the next?

[Lowrider]

I went through my 79 Ranchero 351m a couple years ago and ended up with about the same oil consumption you have. Had it bored .030 over, 400 crank & pistons and had the heads gone through. Used oil right from the start. Finally got around to checking it a few weeks ago. No leaks. Wet and dry compression test were good. After scratching my head for a bit I decided to replace the valve seals. The shop put the plastic valve seals on, so I replace them with a set of rubber seals I had laying around. Hasn't used a drop of oil since.

[cleandan]

Most recent update.
My friend disconnected the PCV system and is now no longer using any oil. He has not yet logged enough miles to make this definitive but with such high oil consumption before, and no oil consumption now, the situation looks good.
He says there is basically no oil in the PCV tube or in the bottom of the intake. This seems odd and I am not sure how that much oil can be consumed without leaving big traces...but it is happening here.

The PCV set up has the PCV valve in the oil fill tube on the passenger side front of intake. This is a Ford dual quad intake by the way.
The valve is on the high side of the tube, pointing towards the distributor/carb gap, Teed directly off the tube at a right angle to the fill tube. The PCV valve is sitting at an angle and not flat like on a valve cover. The hose is run from the PCV valve to the front carb base plate.
If nothing else this combo looks like it is not a good choice even though all parts check out as working properly.
As much of a pain in the butt this has been I am somewhat glad it happened because now I know better for future reference.
Again, thank for all help. I honestly appreciate the time and effort and I hope I can return the favor some day.

[ericwevans]

I could be mistaken, but I thought the PCV was supposed to go to a port on the rear of that manifold and only have a breather on the fill tube.

[cleandan]

This Ford intake has no port for a PCV anything. It originally had the rear breather tower.
The front carb, mounted backwards for dual quads, has the usually rear facing 3/8" nipple sticking out front and center and is perfect for a PCV hookup. I am guessing that is why the original installer of this particular system put things where they did.

[Heo]

On a PCV you should have air in to the engine also
Like PCV valve in the rear of intake air in through the filler pipe
or PCV on one valve cover air in through the other valve cover

[ericwevans]

That's what I'm thinking, normally you'd have a road draft tube of the back to draw combustion gases out, breather front to let fresh air in.  Thinking while putting the PCV in the breather may be convenient I doubt it is optimal as it isn't placed to entice fresh air in.

[Heo]

Maybe the result is some "paintgun" effect that sucks the oil out

[cleandan]

The factory style rear breather tower is acting as the "air inlet" on this intake manifold.

[ericwevans]

The valley splash shield doesn't cover the front 1/4 of the valley so it is possible you are getting splash up the fill tube that is being ingested by the PVC.  At the rear it would be protected from splash by the shield.