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Free and Fast Oil Consumption Mod/ Fix in Ten Easy Steps

73K views 134 replies 33 participants last post by  alacran 
#1 · (Edited)
OK, on the CTS board, there are a couple of guys with LY7s that claim they have fixed their oil consumption problem by modding their PCV orifice fitting. I just performed this mod - it is ridiculously easy and fast, and if you are well-equipped (tools, get your mind out of the gutter) it shouldn't cost anything.

The PCV orifice fitting lives in the right (passenger's side) valve cover, in the rear. It has a hose that clips onto it. The fitting is shaped like a PCV valve, only the neck is narrower and the base has two holes instead of one. It has no valve, but is continuously letting crankcase vapors pass.

The mod is to drill out two of the three holes to 7/64". My theory (and I haven't proven it yet) is that by opening up the holes, you reduce the velocity of the air flowing through the system, decreasing the amount of oil in suspension, and thereby reducing the amount burned off.

I used the following tools - a pair of medium sized vice grip pliers, a 7/64" drill bit and drill, a deep well 13mm 3/4" drive socket, a short 3/4" drive extension, a soft mallet, and some sealant (like Permatex Ultra Grey).

Step One: Displace (but do not remove) the engine cover by removing the power steering and oil filler caps and pulling up on the cover (it just snaps off and snaps back in):



Step Two: Remove the PCV hose by pulling back on the clip and pulling up on the hose end:











Step Three: Adjust the vice grip pliers so that it grips the flange on the PCV fitting neck. Don't go crazy or you will be buying a new one, and they are on national back order:





Step Four: Wiggle the vice grips side-to-side while pulling up. This shouldn't take much effort.





 
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#2 · (Edited)
Step Five: Drill out the hole in the neck, and then flip it over and drill out the bigger of the two holes. If you can't tell which one is bigger, get a 1/16" drill bit to compare sizes - the 1/16" will fit in the big hole but not the small one. Make sure you blow out the metal chips with an air hose, and now would be a good time to spray the orifice out with carb cleaner.









Step Six: Make sure you didn't distort the flange excessively. If so, take a nail file to clean it up. Don't worry if it is a little chewed. Take a very small amount of sealant and apply to the base of the orifice fitting - make sure not to slop it on or you will block the holes in the base and make things worse.





Step Seven: Insert the fitting back into the camshaft cover, and use the socket, extension and mallet to firmly seat the fitting. Again, don't go crazy, just enough to drive the fitting home. GM recommends giving the fitting a twist to eliminate leaks from vertical voids in the sealant.



Step Eight: Reconnect the hose, pulling up on it to make sure it is properly seated.



Step Nine: Snap the engine cover back on and replace the power steering and oil filler caps.

Step Ten: Close the hood, have a beer, and enjoy the thought of saving up to $50 in oil between oil changes.
 
#3 ·
Some of those shots are with an extra PCV hose I had, just to clarify how the clip works and how the fitting seats on the flange. The sealing is with an o-ring in the fitting, so the flange is a retainer, not a seal.

I have not tested this mod, but will be monitoring oil consumption. I was up to as much as 1qt per 800 miles. I will, of course, update as I discover more information.

I have a ton more pix if anyone needs any additional information. I hope you find this useful.
 
#7 ·
Excellent write up! Can you keep updated as to if theres any oil usage, and if you notice more gas vapor in the oil? Many thanks.
Not sure what you mean by "gas vapor in the oil", or why you think there would be more. Assuming you mean gasoline in the oil, I don't think that would be an issue since these engines are fuel injected and the engine is running fine otherwise. The risk, I think, is that the engine sludge more with lower PCV velocity, but since I have committed to running nothing but Pennzoil Platinum synthetic on a 5000 to 7500 OCI, I am pretty sure that's not going to be a concern.
 
#6 ·
My guess is that they didn't anticipate or think it their responsibility if 1) engines weren't broken in properly (mine wasn't, though I knew better) or 2) oil selection recommendations weren't rigorously followed (I used lots of dino oil in this engine).

In my opinion, there are too many people out there who don't have a problem with their engine to chalk this up to a design issue. I think engines that aren't broken in or maintained right have too much blowby with too much PCV velocity, allowing too much oil to be in suspension and to be drawn into the intake manifold.
 
#9 · (Edited)
The PCV (pre crankcase ventilation) needs to ventilate and stay ahead of the unburnt fuel and gasses from the motor. When it does not work (low CFM) correctly it contaminates and breaks down the oil. This can explain oil consumption. The mod may increase CFM but I would change my PCV valve after every oil change. I would also clean the inside of the vacuum lines going to the PCV valve to help with the air flow. Also oil in the intake manifold may also be a bad PCV valve.




my 2 cents
 
#10 ·
Phoenix understands it!!! Most only think of the release of crankcase pressure. Here is a more detailed expalnation:

Understanding oil contamination from combustion byproducts




The evac system is not for the environment....it is to keep the engine alive and wear free as long as possible. Your not alone and 99% of car owners never think about it or realize whats happening over time. And yes, most will drive 50-75-100k plus miles and never know the damage gradually being done.

My qualifications?

over 35 years building race and performance engines.
Mechanical & Automotive engineer by trade
Graduate of the Reher Morrison Racing engine building school (one of the most respected in the world and a GM R&D contractor).
Owner and driver of drag teams with multiple Divisional, National & World championships in both NHRA & IHRA in several classes (this is where every minute detail in an engine matters)
And I tear down and build most every kind/brand of motor imaginable (except diesel) on a weekly basis.

So here goes:

Every motor has a certain amount of blow-by, the bigger the CI & the more boost the more blow-by (with everything else assumed is equal and no piston/ring/cylinder issue).

Most only look at the crankcase pressure portion and deal with that and that is only a small part of the crankcase evac systems function. The most important is the flushing & removal of the harmful combustion products before they have a chance to condense & settle into the crankcase oil.

These consist of:

Unburnt fuel
Carbon monoxide
water vapor
carbon particles
and several other harmful compounds that when mixed in the crankcase produce Sulfuric acid and as that accumulates past a certain PPM the bearing surfaces, wrist pins, and crank journals begin to be etched and start to damage. This is gradual of course so that’s why like you, most never realize whats happening.

The other very harmful byproduct is the very abrasive carbon particles (near diamond-like in abrasiveness) that many are to small to be caught by the oil filter and accelerate wear as well.

If you have a good cross flow of filtered fresh air entering one side of the crankcase (best is through a flow controlled breather), say the pass side oil fill cap, that fresh air will travel through the pass side valve cover, around the rockers, down the pushrod valley, through the center of the crankcase, (now on the LS6/2/3 valley cover with the fixed orifice it exits there drawn by vacuum so 1/2 the engine is still stagnant with foul compounds...especially the drivers side rocker area) up the drivers side pushrod valley, past the rockers and exits the rear of the drivers side valve cover flushing and pulling the compounds out BEFORE they can settle and condense into the crankcase. Now with out that flow the compounds settle and mix with the oil every time the engine cools. When started and run to operating temp the volatile of those are "flashed off" and again could be evacuated but if just venting with breathers, ONLY the excess crankcase pressure will exit and very little of the harmful compound mix goes with it and once the abrasive carbon particles mix with the oil they are there to stay reducing the protection your oil provides. Now if changing your oil after every track event then this is not an issue. But with a street driven car it is and I can tell you to just look at how dirt your oil gets as far as coloration when you eliminate the evacuation portion of a PCV system, but that tells very little. Send in an oil sample to a good analysis lab and the report back will verify everything I'm saying. The over the road trucking industry does this as a rule, and we do with our race engines as well looking for metal content that tells us a bearing is going away before we could ever detect it and knowing to freshen before a catastrophic failure.

Now back to the LS engine. Any built, big cube, or FI motor cannot breath using the valley cover fixed orifice as it is far to restrictive and excess pressure is a given. So we never use the valley cover vent tube but draw from the rear of the drivers side valve cover.

Now we come to the issue of FI builds that pressurize the intake manifold. Turbo or front mount centri SC systems, the problem with the OEM style system is as soon as you are under boost and the intake is under positive atmosphere you are pressurizing the crankcase directly via the vacuum nipple that evacs under non boost.

The only true solution for street driven cars is a oil separating crankcase evac system that will provide proper, continuous evac while operating under non-boost via the intake vacuum, and as soon as it senses pressurization a check valve senses this and closes blocking any chance of crankcase pressurization. Then as this happens a secondary valve opens and uses the suction/vacuum of the head unit to continue evacuation while the separating can traps & removes all the oil in suspension allowing only the gasses that do not effect the energy released per explosive event (you do NOT want ANY oil entering the intake air charge or residue/varnish forming on the compressor wheels throwing them off balance).

No oil caused detonation, no shortened engine life/increased wear, and the best of everything you need for the motor to perform properly & last as long as possible.
 
#12 · (Edited)
Phoenix understands it!!!
Actually, I don't think so. It's not a valve, it's an orifice. And I think making the hole bigger reduces, not increases, the PCV velocity. The oil is not magically "breaking down" and evaporating - I doubt oil does that in these engines. I think it more likely that the oil is being consumed because it is being held in suspension in the crankcase vapors due to high vapor velocity.

All I can say is that others who claim to have done this mod have claimed it cured their oil consumption after running the mod for thousands of miles without any ill effects and without any other mods.

Not trying to be cranky (no pun intended), but I was hoping this thread would be an instruction help those wanting to do the mod, and not a dissertation on crankcase ventilation theory.
 
#14 ·
Then why does the factory solution of re-ring and valve stem seals etc. seem to always cure the oil consumption problem. I have never seen a report that it didn't. ????????? :poke:
 
#15 ·
ktr-sb is right, crankcase ventilation used to be (pre1965) a draft tube and a vented cap or caps in the valve cover(s) or a vented cap over the pushrod valley area. Positive Crankcase Ventilation was so named because engine vacuum was used to draw out the blowby gasses and re-introduce them to the combustion process. Works fine when gasses/fumes only are drawn in, but when liquid oil itself gets pulled in along with the fumes problems develop, oil doesn't burn cleanly and contributes to carbon build-up and other problems. slowing down the speed of the blowby being pulled by the engine vacuum hopefully slows down or stops the flow of oil that gets pulled along with the gasses/fumes. A different, better baffling system design would have been nice when this V6 was being developed.
 
#20 ·
A different, better baffling system design would have been nice when this V6 was being developed.
There's a CTS owner who pulled the valve cover and installed a baffle and a PCV valve, which he says cured his oil consumption problem. The mod I've shown here is cheaper, easier and quicker. Let's see if it works.

Before you slam the engineers, it helps to realize that PCV is not an exact science, and the more baffles, the more surfaces for temperature and air flow differentials that encourage sludging.

Like I say, when properly maintained these are extremely reliable engines. I got 161K out of mine before the chains needed to be replaced, and if the oil consumption issue improves, I expect to get at least that many more before cracking the motor open again.
 
#23 ·
GM recommends it:



They recommended the same sealant for the engine front cover, and I used Permatex Ultra Grey. It beaded perfectly and I have no leaks or seepage thousands of miles later.

I used Ultra Black on the PCV fitting since it was handy. I imagine any high quality RTV would work fine.

Thanks for bringing this thread back on topic.
 
#26 ·
Sure. The nice thing about this mod is that all you have to do to bring it to stock is replace the fitting with the OEM one, which are hard to get but run about $15.00. The PCV valve/ baffle mod is pretty involved, requiring finding the right sized PCV valve, making and cutting a baffle, and somehow securing it in a way that doesn't come apart under high heat, high vibration conditions. Two other relative disadvantages of the PCV valve/ baffle mod are the need to remove the intake manifold upper section to remove the camshaft cover, and (as with every other mod, including catch cans) the need for additional maintenance of the mod.
 
#28 ·
The catchcan stops the oil from ingesting into the intake air charge, it does not stop oil consumption. This mod (the drill mod) should be done no matter what as it will decress oil consumption. But take your tube from the fixed orfice/PCV and install a cleat glass $10 inline fuel filter between the orfice and the IM and you will see all the oil still ingesting and causing issues (gunk on valve build up, piston & combustion chamber carbon issues, detonation causing less power /fuel economy) all need a good functioning can. These are 2 separate issues.

And phoenix has it understood except the fixed orfice is technicall not a PCV valve as it is fixed.
 
#30 ·
The catchcan stops the oil from ingesting into the intake air charge, it does not stop oil consumption.
Which is why, respectfully, I asked that it not be a part of this conversation, thanks.

This mod (the drill mod) should be done no matter what as it will decress oil consumption.
Not sure what "decress" means, but if it means "decrease," I would be interested to know how you know this, and why you haven't done as much to publicize this free, fast and easy repair as much as you have to publicize the product that you sell. I don't mean to be disrespectful, but in the years I have read this forum, I have seen much about oil consumption and very little until recently about this mod. And mine is the first pictorial that I am aware of. I know you are an authorized vendor and a lot of people respect your opinion, but it seems that so many engines could have been saved if more were done to publicize a known fix like this.

But take your tube from the fixed orfice/PCV and install a cleat glass $10 inline fuel filter between the orfice and the IM and you will see all the oil still ingesting and causing issues (gunk on valve build up, piston & combustion chamber carbon issues, detonation causing less power /fuel economy) all need a good functioning can.
With all due respect, I think this borders on a scare tactic. Concentrating engine deposits in a catch can that does not replicate the interior of an engine simply gives a skewed picture, especially if that can provides surfaces for vapors to cool and condensates to form that otherwise wouldn't. At any given moment, on a properly maintained engine running top tier gas, I would venture to say those "contaminates" are virtually nil. I would be more interested in a sample taken from such an engine with a normal factory PCV system while it is running.

After 161K miles of using the same spark plugs, factory OCIs, and occasional conventional oil use, I had NO valve deposits of any consequence, no driveability concerns, no detontation and very light deposits in the intake manifold.

I would be very interested in seeing the dyno and durability test results for a properly maintained, properly fueled engine with and without a catch can.


And phoenix has it understood except the fixed orfice is technicall not a PCV valve as it is fixed.
There is a vast difference between a PCV valve and a fitting with orifice, one that no engineer I know would call a technicality. One has moving parts and requires servicing, the other doesn't. Moreoever, I carefully inspected my PCV hoses and they were clear, despite Phoenix's guess. A lot of what he says about excessive amounts of fuel ending up in the oil applied back in the days of carburetion and chokes. Those days are gone. And as I and others have posted previously (with pictures), the PCV fitting's orifices will get restricted (but not plugged) with sludge, but cleaning is a relatively simple process of spraying carb or other engine-safe cleaner down the fitting's inlet. Replacing it on every oil change would be a foolish waste of money.

Listen, I don't enjoy quarreling with anyone, especially anyone who has a loyal following and has made tons of money off of selling stuff for these engines. I am just trying to save some people some money, and empower them with correct information. Sorry if I gored anyone's ox.
 
#32 ·
. . . but the thing I dislike so very much on this or any forum is incorrect information.
Lol, I knew I was throwing out red meat. I know this guy sells catch cans for a living, as well as rebuilds Corvette motors, etc, but I've always said that if you can't explain legitimate questions without jargon, and back up what you say with data, you might as well not be saying it at all. And darn it, I think spelling and grammar counts when you are communicating with the written word, lol.

I just want to help people out - that's why I take twice as long to work on my cars to pause and take pix. I value experience as much as the next guy, and I can thump my chest too, but I just want to understand what's actually going on, and not read some WAGs or stuff that applies to other engines.
 
#38 ·
Where have I not posted the data and answered all questions with proof to back it up?

Lol. Yeah, finding out I had to pull the intake to replace the plugs gave me ample cause to procrastinate until the timing chain noise scared me so bad I no longer had any choice. Replaced 'em when I did the chains:




And like I said, the valves were clean and intake had minimal buildup - you can see where the high quality (Shell) fuel kept the scary oil off the valves and off the inside of my intake:



Presumably, that same fuel somehow made its way into the combustion chamber, where it also kept the pistons clean.
This shows clean valves that appear to have been in a non DI motor running top tier fuel and I suspect upper induction cleaning. And it shows how port injected motors benefit from these additives where DI motors do not.

And for those looking for data, here is (reportedly) a used oil analysis on a GM V-8 that went 13K miles on an oil change. Note that it has no fuel in the oil. In fact, "No contamination was found."



On the other hand, here is one with the same engine, reportedly (by the owner) with a catch can, that DOES have gasoline in the oil:



. . . just sayin . . . .
As I stated if you had actually read the posts I made.....the vast majority of catchcans do little to stop this.....most let as much through as they catch, and that is why I posted all the data on the ones that actually do work.

I get very few sales from being a vendor on this forum.....propbably less than $200 a month and average $40-60k from the rest of our sales outlets...most in the dealer network.

Any that want specific facts, pictures, and answers in detail on any question...ask. And if this is not what the OP wants then lets start another thread.
 
#34 · (Edited)
Lol. Yeah, finding out I had to pull the intake to replace the plugs gave me ample cause to procrastinate until the timing chain noise scared me so bad I no longer had any choice. Replaced 'em when I did the chains:




And like I said, the valves were clean and intake had minimal buildup - you can see where the high quality (Shell) fuel kept the scary oil off the valves and off the inside of my intake:



Presumably, that same fuel somehow made its way into the combustion chamber, where it also kept the pistons clean.
 
#35 · (Edited)
And for those looking for data, here is (reportedly) a used oil analysis on a GM V-8 that went 13K miles on an oil change. Note that it has no fuel in the oil. In fact, "No contamination was found."



On the other hand, here is one with the same engine, reportedly (by the owner) with a catch can, that DOES have gasoline in the oil:



. . . just sayin . . . .
 
#36 ·
I'm not saying anyone is wrong or anything I just hate when random non-fact based things are thrown out on the forum and it spreads, no saying anyone threw out non-fact, I was just saying.

Now I am getting off topic, sorry, I like to keep threads on topic and not ruin the OP path and topic. God bless the new guys full of questions but start a thread if you want to stray so it is on topic and easy to find down the road when people search, even though they don't search.....
 
#39 · (Edited)
"pulling back on the clip and pulling up on the hose end"

I can't get the fitting off. There's an identical fitting that goes onto some sort of port right after the MAF but I couldn't figure out how to get that one either.

Is it some sort of latch? Friction fit? I don't see any pieces inside that move relative to the fitting itself.

EDIT: I can see how it opens up now. Time to put it in practice...
 
#40 ·
Pro tip: push down the fitting before trying to open the latch. If you try to open the latch if the fitting is stuck upward, it will jam and you will hate yourself. Once it's down, the latch opens easily.

I rate this mod easy-to-almost impossible depending on how generous your breather fitting is. I could not remove the breather fitting since there is no space (on the CTS) to apply or leverage a full body pull, and locking pliers typically have nothing on them that facilitates pulling. I can deadlift 270+ and I could not get the breather to budge (the whole car was shaking, etc.). I did get it to rotate slightly, though.

****ing wire looms press down HARD into your left forearm, too.
 
#43 ·
Yes it is....and here is my last post giving 3rd party industry technical info on the subject.



Some more good reading:

Crankcase ventilation system


From Wikipedia, the free encyclopedia


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A crankcase ventilation system is a way for gases to escape in a controlled manner from the crankcase of an internal combustion engine.

This is necessary because internal combustion inevitably involves a small but continual amount of blow-by, which occurs when some of the gases from the combustion leak past the piston rings (that is, blow by them) to end up inside the crankcase.





Contents
[hide] 1 Early provisions
2 Road draft tube
3 Positive crankcase ventilation (PCV)
4 Components and details
5 Alternatives
6 References
7 External links


[edit] Early provisions





This section does not cite any references or sources. (April 2012)


From the late 19th century through the early 20th, blow-by gases were allowed to find their own way out to the atmosphere past seals and gaskets. It was considered normal for oil to be found both inside and outside an engine, and for oil to drip to the ground in small but constant amounts. This had also been true for steam engines and steam locomotives in the decades before. Even bearing and valve designs generally made little to no provision for keeping oil or waste gases contained. Sealed bearings and valve covers were for special applications only. Gaskets and shaft seals were meant to limit loss of oil, but they were usually not expected to entirely prevent it. On internal combustion engines, the hydrocarbon-rich blow-by gases would diffuse through the oil in the seals and gaskets into the atmosphere. Engines with high amounts of blow-by (e.g., worn out ones, or ones not well built to begin with) would leak profusely via those routes.

[edit] Road draft tube

The first refinement in crankcase ventilation was the road draft tube, which is a pipe running from a high location contiguous to the crankcase (such as the side of the engine block, or the valve cover on an overhead valve engine) down to an open end facing down and located in the vehicle's slipstream. When the vehicle is moving, airflow across the open end of the tube creates a draft that pulls gases out of the crankcase. The high location of the engine end of the pipe minimises liquid oil loss. An air inlet path to the crankcase, called the breather and often incorporated into the oil filler cap, meant that when a draft was generated at the tube, fresh air swept through the crankcase to clear out the blow-by gases.[1]

The road draft tube, though simple, has shortcomings: it does not function when the vehicle is moving too slowly to create a draft, so postal and other slow-moving delivery vehicles tended to suffer rapid buildup of engine sludge due to poor crankcase ventilation. And non-road vehicles such as boats never generated a draft on the tube, no matter how fast they were going.[1] The draft tube discharged the crankcase gases, composed largely of unburnt hydrocarbons, directly into the air. This created pollution as well as objectionable odors.[1] Moreover, the draft tube could become clogged with snow or ice, in which case crankcase pressure would build and cause oil leaks and gasket failure.[2]

[edit] Positive crankcase ventilation (PCV)

During World War II, however, a different type of crankcase ventilation had to be invented to allow tank engines to operate during deep fording operations, where the normal draft tube ventilator would have allowed water to enter the crankcase and destroy the engine. The PCV system and its control valve were invented to meet this need, but no need for it on automobiles was recognised.

In 1952, Professor A. J. Haagen-Smit, of the California Institute of Technology at Pasadena, postulated that unburned hydrocarbons were a primary constituent of smog, and that gasoline powered automobiles were a major source of those hydrocarbons. After some investigation by the GM Research Laboratory (led by Dr. Lloyd L. Withrow), it was discovered in 1958 that the road draft tube was a major source, about half, of the hydrocarbons coming from the automobile. GM's Cadillac Division, which had built many tanks during WWII, recognized that installation of PCV on vehicles could bring the first major reduction in automotive hydrocarbon emissions. After confirming the PCV valves' effectiveness at hydrocarbon reduction, GM offered the PCV solution to the entire U.S. automobile industry, royalty free, through its trade association, the Automobile Manufacturers Association (AMA).[citation needed] The PCV system thus became the first real vehicle emissions control device.

Positive crankcase ventilation was first installed on a widespread basis by law on all new 1961-model cars first sold in California. The following year, New York required it. By 1964, most new cars sold in the U.S. were so equipped by voluntary industry action so as not to have to make multiple state-specific versions of vehicles. PCV quickly became standard equipment on all vehicles worldwide because of its benefits not only in emissions reduction but also in engine internal cleanliness and oil lifespan.[3][1]

In 1967, several years after its introduction into production, the PCV system became the subject of a U.S. federal grand jury investigation, when it was alleged by some industry critics that the AMA was conspiring to keep several such smog reduction devices on the shelf to delay further smog control. After eighteen months of investigation by U.S. Attorney Samuel Flatow, the grand jury returned a "no-bill" decision, clearing the AMA, but resulting in a "Consent Decree" that all U.S. automobile companies agreed not to work jointly on smog control activities for a period of ten years.[citation needed]

In the decades since, legislation and regulation of vehicular emissions has tightened substantially, and the toxic emissions of cars and light trucks have decreased substantially. Today's petrol engines continue to use PCV systems.

[edit] Components and details





PCV valve on Ford Taunus V4 engine in a Saab 96, between left valve cover and intermediate flange on intake manifold
The PCV valve is only one part of the PCV system, which is essentially a variable and calibrated air leak, whereby the engine returns its crankcase combustion gases. Instead of the gases being vented to the atmosphere, gases are fed back into the intake manifold, to re-enter the combustion chamber as part of a fresh charge of air and fuel. The PCV system is not a classical "vacuum leak". All the air collected by the air cleaner (and metered by the mass flow sensor, on a fuel injected engine) goes through the intake manifold. The PCV system just diverts a small percentage of this air via the breather to the crankcase before allowing it to be drawn back in to the intake tract again. It is an "open system" in that fresh exterior air is continuously used to flush contaminants from the crankcase and into the combustion chamber.

The system relies on the fact that, while the engine is running under light load and moderate throttle opening, the intake manifold's air pressure is always less than crankcase air pressure, see manifold vacuum. The lower pressure of the intake manifold draws air towards it, pulling air from the breather through the crankcase (where it dilutes and mixes with combustion gases), through the PCV valve, and into the intake manifold.

The PCV system usually consists of the breather tube and the PCV valve. The breather tube connects the crankcase to a clean source of fresh air—the air cleaner body. Usually, clean air from the air cleaner flows into this tube and into the engine after passing through a screen, baffle, or other simple system to arrest a flame front, to prevent a potentially explosive atmosphere within the engine crank case from being ignited from a back-fire in to the intake manifold. The baffle, filter, or screen also traps oil mist, and keeps it inside the engine.

Once inside the engine, the air circulates around the interior of the engine, picking up and clearing away combustion byproduct gases, including a large amount of water vapor which includes dissolved chemical combustion byproducts, then exits through another simple baffle, screen, or mesh to trap oil droplets before being drawn out through the PCV valve, and into the intake manifold. On some PCV systems, this oil baffling takes place in a discrete replaceable part called the oil separator.

During the mid 1960s, substantial work was completed on an entirely independent crankcase ventilation system. The Engine Ventilation System had its own air intake filter, a sizable crankcase gases filter, condensate chamber, and highly engineered air flow valve.[citation needed] The system recycles clean water vapor, filters light oil, and filters air into the intake system before the carburetor, resulting in lower carbon monoxide and hydrocarbon emissions and extended engine oil life. Ford Motor Company made this system a requirement on all its material handling equipment (lift trucks) in 1971. This system was also used extensively on over-the-road diesel trucks and irrigation pumps. The AMA's choice[clarification needed] of catalytic converter made automotive use unlikely.[citation needed]

The PCV valve connects the crankcase to the intake manifold from a location more-or-less opposite the breather connection. Typical locations include the opposite valve cover that the breather tube connects to on a V engine. A typical location is the valve cover(s), although some engines place the valve in locations far from the valve cover. The valve is simple, but actually performs a complicated control function. An internal restrictor (generally a cone or ball) is held in "normal" (engine off, zero vacuum) position with a light spring, exposing the full size of the PCV opening to the intake manifold. With the engine running, the tapered end of the cone is drawn towards the opening in the PCV valve by manifold vacuum, restricting the opening proportionate to the level of engine vacuum vs. spring tension. At idle, the intake manifold vacuum is near maximum. It is at this time the least amount of blow by is actually occurring, so the PCV valve provides the largest amount of (but not complete) restriction. As engine load increases, vacuum on the valve decreases proportionally and blow by increases proportionally. With a lower level of vacuum, the spring returns the cone to the "open" position to allow more air flow. At full throttle, vacuum is much reduced, down to between 1.5 and 3" Hg. At this point the PCV valve is nearly useless, and most combustion gases escape via the "breather tube" where they are then drawn in to the engine's intake manifold anyway.






Should the intake manifold's pressure be higher than that of the crankcase (which can happen in a turbocharged engine, or under certain conditions, such as an intake backfire), the PCV valve closes to prevent reversal of the exhausted air back into the crankcase again. In many cases PCV valves were only used for a few years, the function being taken over by a port on constant depression carburetors such as the SU. This has no moving parts or diaphragm to jam, block or rip like many PCV valves. It also doesn't have a 'one-way' function but the lack of it was never a problem in intake backfire.

It is critical that the parts of the PCV system be kept clean and open, otherwise air flow will be insufficient. A plugged or malfunctioning PCV system will eventually damage an engine. PCV problems are primarily due to neglect or poor maintenance, typically engine oil change intervals that are inadequate for the engine's driving conditions. A poorly-maintained engine's PCV system will eventually become contaminated with sludge, causing serious problems. If the engine's lubricating oil is changed with adequate frequency, the PCV system will remain clear practically for the life of the engine. However, since the valve is operating continuously as one operates the vehicle, it will fail over time. Typical maintenance schedules for gasoline engines include PCV valve replacement whenever the air filter or spark plugs are replaced. The long life of the valve despite the harsh operating environment is due to the trace amount of oil droplets suspended in the air that flows through the valve that keep it lubricated.

[edit] Alternatives

Not all petrol engines have PCV valves. Engines not subject to emission controls, such as certain off-road engines, retain road draft tubes. Dragsters use a scavenger system and venturi tube in the exhaust to draw out combustion gases and maintain a small amount of vacuum in the crankcase to prevent oil leaks on to the race track. Small gasoline two stroke engines use the crankcase to partially compress incoming air. All blow by in these engines is burned in the regular flow of air and fuel through the engine. Many small four-cycle engines such as lawn mower engines and small gasoline generators, simply use a draft tube connected to the intake, between the air filter and carburetor, to route all blow by back into the intake mixture. The higher operating temperature of these small engines has a side effect of preventing large amounts of water vapor and light hydrocarbons from condensing in the engine oil.

[edit] References

1.^ a b c d Rosen (Ed.), Erwin M. (1975). The Peterson automotive troubleshooting & repair manual. Grosset & Dunlap, Inc.. ISBN 978-0-448-11946-5.
2.^ Gus Saves a Friend from a Snow Job, Popular Science, February 1966
3.^ NAPA Echlin Service Bulletin: Crankcase and Exhaust Emission Control; February 1968
 
#44 ·
And from the British:

The usual PCV systems come in two basic flavors, and I'll distinguish them here by referring to them as American and British respectively, due to the prevalence of their use by manufacturers in each country, and in particular in distinguishing LBC's from Detroit iron.

In the British system, which is the more straightforward of the two, manifold vacuum is plumbed directly to the crankcase using a 0.5" or 0.75" diameter line. An orifice of typically 0.030" or less is provided on a line feeding fresh air into the crankcase. Sometimes this line draws vapors from a vapor recovery canister as well, thereby purging the canister and feeding those vapors indirectly into the engine intake, and sometimes this orifice is contained in an oil filler cap, but for the purposes of PCV it functions the same either way. It does however have the potential to either enrich or lean the idle mixture to a limited degree. The manifold vacuum purges the crankcase of blowby fumes. By placing the crankcase under vacuum, a metered quantity of fresh air is drawn into the crankcase through the orifice... at least at idle and part throttle. As the throttle opens and engine load increase, blowby also increases proportionally until at some point the crankcase transitions from vacuum to positive pressure. This may not occur with a new engine in good condition using a larger vacuum line, but it certainly will with an engine having significant mileage. When the crankcase is at positive pressure, nothing changes on the vacuum side other than the volume of gasses going into the intake, but on the orifice side the flow reverses. This is usually not particularly significant due to the small size, but can contaminate the carbon in the vacuum canister over the course of time.

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American systems use a large diameter vent line to the atmosphere, usually running from a valve cover to a location in the air filter housing, and a smaller diameter line to the intake manifold, usually 0.3125" to 0.375" in diameter. This system restricts the amount of combustible air which enters the engine with a PCV valve rather than an orifice, and it is placed in this intake line. The PCV valve is pretty unique in that it allows full flow at low pressure differentials across the valve and a metered restriction above that level. It also shuts off flow in the reverse direction, thereby eliminating the need for a flame trap. This is done by using a shuttle inside the valve which I'll return to shortly, as this is the most misunderstood part of the system.

The crankcase is never under vacuum but can become slightly pressurized. The large diameter vent line allows fresh air into the crankcase and also allows excess blowby to vent into the air cleaner housing through a flame arrestor where they are ingested by the engine, whenever engine loads and throttle openings are great. Under part throttle the PCV valve is open due to the lower vacuum applied across it and the lower level of blowby so most if not all of the blowby is sucked into the intake, drawing fresh air into the engine in the process and also tending to lean out the intake mixture during cruise. During idle there is enough vacuum to shuttle the PCV valve to the metered position and there is usually very little blowby so most of that is ingested along with a small amount of fresh air which is accounted for by adjustment of the idle mixture screws. This is one reason the idle mixture has to be adjusted as the rings wear. Under heavy throttle, although the level of vacuum drops to near zero, should the level of blowby become great enough the shuttle will shut down the flow to the metered level, diverting most of the blowby to the air cleaner and ingesting only a metered amount of blowby through the PCV valve.

The effect of routing these gasses through the air cleaner is to enrich the intake mixture proportionally because the carb doesn't know the difference between fresh air and recycled combustion by-products. So it is interesting that the PCV system helps to give us a lean cruise and a rich WOT, but there is little or no correlation between PCV, carburetor, and volume of blowby other than the initial calibrations of the carb and PCV valve and no mechanism to account for engine wear other than the shuttle valve and idle mixture screws. The interesting thing about this is that the same PCV system is still in use with very little modification on our newer fuel injected engines, although they do have a feedback mechanism in the form of an oxygen sensor.

These systems work quite well normally, but things tend to get interesting once performance modifications are made. Often the PCV systems are unintentionally modified to the point that they can no longer function properly, and this is particularly common with aftermarket intakes, air filters, valve covers, forced induction and the like. It is still possible on almost any performance engine to design and tune for a PCV system that works properly and this is especially important in a street driven car. For all out performance it is less of a consideration and in fact the blowby fumes do dilute the intake charge somewhat, so in these cases a simple crankcase vent is often used, harking back to the early days, with all their attendant inconveniences. Often modifications are made to the system unintentionally, in the quest for more performance and a better appearance, and this can result in problems. One of the most bothersome is pressurization of the crankcase, with symptoms of excess oil sprayed about the engine compartment in various places as it is forced past gaskets and seals. Another is the chance of a crankcase explosion should the need for a flame trap be overlooked. Then of course, any improperly functioning system will have a need for more frequent oil changes, as the combustion byproducts contaminate the oil more rapidly.





For your street driven car there are answers. Sometimes the British system is more appropriate, and sometimes American, but it's best to keep in mind how each one operates and not try to mix the two. When fitting an open element air cleaner onto a typical American 4-barrel carbureted V8, for instance, it's quite easy to install the vent line to the base of the air cleaner inside the element, thereby keeping the system intact. Things aren't quite so neat and clean when fitting a similar air cleaner on a Rover V8, because Rover engines were originally set up with an orifice-type system. Some of these are easily changed over and some are not, depending on the fittings on the rocker covers. Bear in mind that the large vent line of 0.625" or possibly 0.75" in some cases cannot be replaced with a 0.375" hose, or even two of them. Flow increases by the square of the diameter, meaning that a 2" pipe flows four times as much as a 1" pipe. So you would need four 0.375" lines to match one 0.75" line. If your valvecovers do not have the proper fittings and you are not willing to add larger ones to them then you may need a larger line to the crankcase in an alternate location. Early SBC's had a vent line that went through the block web behind the intake manifold. A large diameter tube rising from the pan may be another option. You might use the mechanical fuel pump mounting boss. Or you may be able to use the orifice system, bearing in mind that using smaller lines will cause it to operate under pressure more than it might otherwise. This may require recalibration of your carburetor due to the differences mentioned above, or it may be possible to find a suitable carburetor calibrated for the orifice system, since some British cars were available with a four barrel carburetor. There are other cases where an orifice system is a good choice, such as any induction system where the throttle body is at the inlet of the system. This might be the case with an IR setup or where an engine is supercharged. In these situations there is no practical way to locate the vent tube, and therefore no way to ingest the excess blowby fumes. The solution is to port the crankcase to manifold vacuum (or inlet vacuum in the case of a blower) and use the orifice to restrict flow into the crankcase and subsequent leaning of the intake mixture. It is worth noting here that often EFI systems take control of the PCV system, such as by including a purge valve for the emissions canister, allowing options such as pulling fresh air in at idle to give more precise control of the mixture. Some of these systems may be able to divert PCV intake on WOT for maximum power output. WARNING: All lines from crankcase to intake system must have some form of flame arrester! To overlook this is to invite a crankcase explosion, which in the best possible scenario will have you replacing your lifter valley pan.

Finally, we have the alternative systems, the most familiar being the collector scavenger tube. These are really not suitable for a street driven application because of two things: mufflers, and the fact that they do not work well at idle. For racing it's a good idea, but once you add the restriction of a muffler you have created backpressure which will reverse the flow in the scavenger tube and make the system ineffective. Another option is an external scavenger pump. These tend to be a more complicated solution, but are another possibility that may have merit in special situations. Theoretically it would be possible to evacuate the crankcase using positive pressure and this would tend to lead to seal problems, but if those woes were overcome one might even find a way to route forced induction through the crankcase on its way to the cylinder, provided an adequate air/oil separator were designed. Two stroke engines inherently use this principle, simply burning the oil as they go.

So that's the basic lowdown. No doubt there are details that I've left out but it's enough to give the average person the picture. Hopefully it's enough to help sort through the tangled mess and maze of confusion that typically surrounds these systems
 
#47 ·
Let's close this off. I am 100% sure that this approach does not solve the oil consumption so don't waste your time with it. If it solved the problem, do you not think GM would have issued a recall to replace the PVC valves etc? GM is obviously aware of the problem, has addressed it to the best of its abilities, but ultimately, a preventative design measure would be too expensive to implement.
 
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