PCV trap update

[UNC017]

A few months ago, I posted this thread:
https://bobistheoilguy.com/forums/posts/1727358/

about adding a PCV trap to my wife's PT (about 50,000 miles). Before the trap, it would routinely go through a quart of oil in ~1200 miles, and oil consumption varied depending on driving cycle- city/short trips vs highway.

Sunday, I pulled an oil sample at 6800 miles on the current fill. Including the oil removed for the sample that brings the total make-up oil to ONE quart in 6800 miles (Mobil 1 0w30AFE). And I've observed no spikes in consumption with long intervals of city driving or with the 3 ~1000 mile highway trips on current oil fill. If the TBN comes back OK I'm headed for 10k miles on the OCI, FWIW.

That exceeds my wildest expectations for the performance of the oil trap. Amazing what such a little change can do- and it just goes to prove that high oil consumption doesn't always indicate a mechanical problem.

 

[Drew99GT]

Where did you buy that fuel filter and what part of it did you drill out?

 

[UNC017]

Originally Posted By: Drew99GT
Where did you buy that fuel filter and what part of it did you drill out?


Got it at Pep Boys but I've seen them hanging on the "performance parts" display at lots of stores. They're pretty cheesy- I'd never actually use one for fuel on anything bigger than a Briggs&Stratton

The way its made, there's a central aluminum tube that is plugged in the center. The end caps screw onto the central tube and hold the assembly together, and the inlet/outlet fittings open into the tube. That tube is then cross-drilled on either side of the central plug so that the fuel (or air, in my case) squirts out the sides of the tube, flows up the glass cylinder, and then back into the tube. I enlarged the cross-drilled holes (and I think I even added a pair) to slow the air down.

 

[Drew99GT]

I'm sick as a dog and off from work. I shall be heading to Pep Boys within the hour. I'm bored!

 

[mechtech2]

PCV systems don't normally suck oil through them - they are not supposed to. You should get only a tiny amount that can't be measured.
They suck vapors from blowby.
Maybe the old system did not vent properly, and ring control was compromised, causing poor oil control .

 

[Gary Allan]

As we can see, not EVERYTHING OEM engineered is doing the best job possible.

They must have given the PCV venting to the plebe engineer in the group. Either that or the senior engineer that they were trying to push out with giving him insultingly simple tasks. He may have decided to leave his mark in a less than stellar manner.

 

[UNC017]

Originally Posted By: mechtech2
PCV systems don't normally suck oil through them - they are not supposed to. You should get only a tiny amount that can't be measured.
They suck vapors from blowby.
Maybe the old system did not vent properly, and ring control was compromised, causing poor oil control .




In theory you're right. But the crankcase on a car is always chock full of oil spray and mist from moving parts. That mist has to be separated from the vapor, and older PCV systems did a pretty good job just because there were big open spaces in the tops of valve covers where "dead space" would allow the mist to settle out on baffles and drop back into the engine. Today with smaller under hood space, valve covers that practically mold around the moving parts, etc. many OEM PCV systems don't have enough baffling in the valve cover to trap all the oil mist, and/or don't have any low-velocity point in the tubing to allow the mist to settle out. The PT Cruiser is kinda a notorious case. So were some models of the GM F-bodies. If you look at the original PCV setup on the PT Cruiser, the PCV valve screws right into the valve cover, so the high velocity air flow is basically sticking right into a mist-filled region. Then to make matters worse, the hose to the manifold is less than 8 inches long and is horizontal- no separation there either.

 

[SteveSRT8]

lots of modern cars with dry manifold designs have the excessive oil issue.

It's disturbingly common. Especially in the higher power output motors.

 

[mechtech2]

Any car with a 'dry' manifold will suffer from deposits from the PCV system.
This is why I use a catch can.
But this does not mean they are engine oil deposits.
Most newer cars hardly use oil, in total, counting everything.

I know that there are substandard implementations of oil separators/breathers/PCV systems out there.

So keep using what works.

It's just that my first inclination is to fix the problem that allows actual engine oil into the manifold.

 

[UNC017]

Originally Posted By: mechtech2
Any car with a 'dry' manifold will suffer from deposits from the PCV system.
This is why I use a catch can.


But a catch can isn't going to actually CATCH anything but oil mist. The other contaminants are gaseous (combustion byproducts) that just sail right through the catch can for the most part. A *little* bit of them might get entrained and concentrated in the oil mist that gets held there, but most of the bad stuff will never become liquid.

Originally Posted By: mechtech2
It's just that my first inclination is to fix the problem that allows actual engine oil into the manifold.


Which is exactly what a separator does ("catch can" to me implies one that doesn't allow the good oil to drain back to the engine). The only other alternative to an external separator is to go in and perform major surgery on the valve cover to put better dead space/baffling under there, which isn't really feasible on modern engines where the covers hug the moving parts so closely.

 

[SteveSRT8]

I nearly cured this on my 6.1 by experimenting with oils to find the least volatile.

And I agree a can is just a band aid. But a finned one with access to cold air would be better!

 

[mechtech2]

Right. A catch can does not stop everything. It is not perfect.
It is a quick and cheap idea that works.

It sure does make a difference!
My throttle body and manifold stay virtually clean now.
It used to pool in the manifold, and the TB would get deposits.

Others may not get great results, but some is better than nothing.