PCV Line Oil Removal 101:

PCV Line Oil Removal 101:
Having been involved the utilization of compressed air systems and related components
for many years, I became interested in the proliferation of “Oil Catch Cans” in many
different types of vehicles. Could there be a better way to trap oil than the tried and true
methods I’ve grown to know all these years? Let’s take a look at what is going on in that
little PCV tube.
From Wikipedia, we learn that…..
“As an engine runs, the crankcase (containing the crankshaft and other parts) begins to
collect combustion chamber gases that leak past the seals around the pistons. These
combustion gases are sometimes referred to as "blow by" because the combustion
pressure "blows" them "by" the pistons. These gases contain compounds harmful to an
engine, particularly hydrocarbons, which are just unburned fuel. It also contains a
significant amount of water vapor. If allowed to remain in the crankcase, or become too
concentrated, the harmful compounds begin to condense out of the air within the
crankcase and form sludge on the engine's interior surfaces. This can harm the engine as
it tends to clog small inner passages, causing overheating, poor lubrication, and high
emissions levels. To keep the crankcase air as clean as possible, some sort of ventilation
system must be present.
The PCV valve is only one part of the PCV system, which is essentially a closed-loop
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." Remember that all the air collected by the air
cleaner (and metered by the mass air flow sensor, on a fuel injected engine) goes through
the intake manifold anyway. 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.
The system relies on the fact that the intake manifold's air pressure is usually less than
crankcase air pressure. The lower pressure of the manifold forces air to flow 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 consists of: 1) The breather tube , and 2) The PCV valve. The breather
tube connects the crankcase to a clean source of fresh air, such as the air cleaner body.
Usually, clean air from the air cleaner flows in to this tube and in to 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 backfire 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, then
exits through a simple baffle, screen or mesh to trap oil droplets before being drawn out
through the PCV valve.” Mmmmm – obviously in many engines, this “trap” is not
enough to catch ALL the oil droplets.
PCV Line Oil Removal 101 (continued)
PCV valve
“The PCV valve connects the crankcase to the intake manifold from a location more-orless opposite the breather connection. Typical locations include the opposite valve cover
that the breather tube connects to on a V-8 or V-6 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. 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 restriction. As engine
load increases, vacuum on the valve decreases proportionally, and blow by increases
proportionally. Sensing a lower level of vacuum, the PCV valve opens further to allow
more air flow. At full throttle, there is nearly zero vacuum. 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.
Operation
Should the intake manifold's pressure be higher that of the crankcase (which can happen
under certain conditions, such as an intake backfire), the PCV valve closes to prevent
reversal of the exhausted air back into the crankcase again. This is where the positive
comes from in the name. Positive is basically a synonym for one-way.
It is critical that the parts of the PCV system be kept clean and open, otherwise air flow
will not be correct. 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
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PCV Line Oil Removal 101 (continued)
the life of the engine. However, since the valve is constantly changing its resistance to
flow by opening and closing proportionally as one drives a car, it is subject to eventual
wear out over time. Typical maintenance schedules for gasoline engines are to replace the
PVC valve whenever 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. These droplets keep the valve lubricated. This means
that you probably shouldn’t remove all oil before the PCV valve and fortunately,
most oil catch cans are placed in-line after the PCV valve.
Not all gasoline 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 2-cycle
engines use the crank case to compress incoming air. All blow by in these engines is
burned in the regular flow of air and fuel through the engine. Many small 4-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 in
to the intake combustion air. 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 lube oil.”
For some good images of PCV systems, see http://www.autoshop101.com/forms/h63.pdf
Got that info? Good – let’s move on to existing catch can designs.
Most catch cans consist of either a simple, welded aluminum or silicone body, or a
machined rod of aluminum (as the body) with a matching top piece. Some of the more
expensive versions have steel wool mesh inside. While this type is more effective than
the inexpensive, empty type, it is not the best way to trap oil vapors. “What is the best
way to trap oil vapor?” you might ask! We’re almost there – but first, let’s look at….
Particulate filters: In a compressed air system, these filters are typically installed
before aerosol-trapping (coalescing) filters. Particulate filters are designed to trap solid
particle contaminants down to 5 microns and the separation of bulk liquids. The key
work here is “bulk”. This type of filter, which is often found in home supply stores as a
general purpose filter for compressed air systems, removes liquid water and oil.
It does NOT effectively remove air-born oil (aerosols), which is very likely to be
flowing past the PCV valve and into the engine intake. The other thing I can’t mention
enough is the fact that any filter that has a clear, polycarbonate bowl is a bad choice as
an oil catch can for 2 reasons:
1. The typical clear bowl – equipped filter has maximum operating temperature of
120 or 125° F. An LS1 engine bay can reach temperatures beyond 140° F, quite
easily, potentially causing the seal between the bowl and the inlet/outlet
component to leak.
2. Many of these filters are designed for air flow rates of greater than 20 cubic feet
per minute (CFM). Flow rates significantly below this level may allow
particulates and liquids to pass through to the engine intake – something we are
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PCV Line Oil Removal 101 (continued)
trying to avoid. I measured flow from a PCV valve at approx. 36 LPM = 1.8
CFM.
Particulate filter
Coalescing Filters: The oil-removing standard
Coalescing filters rely on mechanical filtration, which means that the flowing particles
collide and eventually adhere to filter fibers.
This type of filter is specifically designed to remove solid particulates, water and oil
aerosols down to .01 micron. Most of the well-known coalescing filter manufacturers,
like Wilkerson use borosilicate glass micro fibers. Compared to simple stainless steel
mesh, they provide “superior filtration efficiency, quick draining, and minimum pressure
drop.” Unlike standard particle filters (like the Home supply $13 specials), airflow is
inside to out. Speaking of the home supply filters that are typically sold in the compressor
accessory area of the store, most are general purpose particulate filters. These filters are
designed to remove bulk liquids and solid particles only. Aerosols such as oils will
typically pass through these filters – right on to your intake manifold. Since they do trap
some of the bulk oil, they arecertainly better than having nothing at all if the right one is
selected. Hint: The clear-bowl filters generally have a maximum operating temperature
of 125 degrees F. This is well below common engine bay temps, so avoid using a filter
having this type of bowl.
Anyway, according to the folks at Wilkerson, “The compressed air/gas passes through
the inner layer of the filter element which acts as an integral prefilter to remove large
contaminants. This gives protection to the layer of high-efficiency filter material which
substantially removes submicronic aerosols and solids from the air flow stream.
The fine liquid particles, including aerosols begin to collect or coalesce, forming larger
droplets. The separated liquid drops from the bottom of the filter element and falls to the
bottom of the filter housing…..” See image, below.
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PCV Line Oil Removal 101 (continued)
“Why then” , you might ask, “won’t catch can makers use this tried and true method of
trapping oil vapors?” That’s a great question, the answer to which I can only guess. My
assumption is that a coarse, relatively inexpensive mesh, such as stainless steel, is more
likely to last longer than a borosilicate filter, primarily because the stainless steel mesh
will not trap as many contaminants/oil and hence, clog as easily. However, I have been
using coalescing filters for many years and have yet to see a filter so clogged that it had
to be replaced. Perhaps a stainless steel-mesh common catch can is similar to run-flat
tires in that they can be a bit safer, but by design, also sacrifice effectivity and therefore,
performance.
An effective, yet inexpensive solution, stage 1
Crucial to picking out the correct coalescing filter is knowing what conditions are
present in your PCV system. I was able to borrow a digital flow meter and measured flow
after the PCV in my LS1 engine. I also measured vacuum pressure by using an
mechanical vacuum gauge that was calibrated in inches of mercury. In order that I choose
a filter than can stand the heat, I measured engine bay temps in a couple of different
places by taping a HOBO data logger underhood and then later extracting temperature
data. Here’s what I found:
Flow at 800 rpm: 36 LPM = 1.27 CFM
Flow at 4000 rpm: 37 LPM = 1.31 CFM
Maximum temp. between right side head and fender during 20 minute ride home on a 75
degree day: 140°F
Maximum temp. in battery compartment during 20 minute ride home on a 75 degree day:
132°F
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PCV Line Oil Removal 101 (continued)
Data Logger
Armed with this information, I called two well-known pneumatic filter manufacturers –
Watts and Parker. (Even though Parker owns Watts, they seem to be treated as separate
businesses.)
Watts recommended their F501-02DHX67 coalescing filter assembly (includes mounting
bracket, part number of assembly without bracket = F501-02DH)
Parker recommended their HN15-4DSJ coalescing filter assembly (no bracket). Because
the Watts unit was a bit less expensive ($43 vs $48). I chose the Watts. However, I am
very confident that either one will perform very well.
Note: These prices are discounted for company purchases. An individual may have to
pay prices that are 20% higher.
Unfortunately, because these filters are designed for low-flow, low-pressure
applications, the bowl that is used in each assembly has a liquid capacity of only 1 oz.
During average driving conditions, this small amount of oil would need to be discarded
every 1000 -1500 miles. For some, this would be 6 months or more. Since I typically pile
on approx. 5000 miles per year, I needed something a bit larger. Therefore, I designed an
extended can and will gladly send anyone who asks, a PDF version of this drawing. You
can extend the length even further if you so desire. Just make sure that you have room for
it in your vehicle. See pics, below.
Zinc body with drain valve
The as-purchased filter assembly. Yes, it is small, but remember, it is designed for lowflow/low pressure applications.
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PCV Line Oil Removal 101 (continued)
Internal filter and plastic retainer
Disassembled components
Extended aluminum body - see
http://www.conceptualpolymer.com/corvette_c5_corner.htm for drawing.
Hose and filter/catch can installation location considerations:
Note: The “out” end of the filter/catch can goes to the throttlebody. This is the end
that is pulling vacuum pressure through the filter. Thus, the “inlet” port of the
filter/catch can is connected to the PCV line.
Some catch can manufacturers instruct buyers to mount their catch cans directly to
cylinder heads or engine blocks. Not only are these locations subjected to high heat, but
the mounting brackets supplied with the catch cans are made of metal, usually steel or
aluminum. Since steel and aluminum are great conductors of heat, these are NOT good
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PCV Line Oil Removal 101 (continued)
locations. Why is staying away from heat important? The most effective coalescing of
vapors into liquids occurs when there is a temperature change (typically, hot-to-cold);
this, all coalescing filter manufacturers recommend that their filters be placed in a cooler
area than the area containing the source of heat from which the airstream originates. The
same holds true for catch cans or true coalescing filters used in automotive
applications.
In other words, KEEP THE FILTER AWAY FROM HEAT! If you MUST mount a
filter bracket or bar to an engine block or cylinder head, use a material that does NOT
conduct heat well. I recommend FR4, a fiberglass/epoxy material that can withstand over
200°F.
My first mounting choice was in the battery compartment area, since this area tends to
be somewhat isolated from the engine heat.
Best location for
filter
Initial location of filter
However, mounting the filter in this area requires that the PCV hose extension will have
to loop upwards. Over time, this may result in some oil puddling in the loop – kinda like
water that sits in an under sink trap.
Plan B will be to mount the filter down toward the front of the engine bay. This is an
ideal area, since the oil-laden air will have to flow downward. Once cleaned of liquid and
aerosols, the air can flow upward and into the intake/throttle body. An added bonus is
that the cleaned air will have a chance to cool before entering the intake, and we all know
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PCV Line Oil Removal 101 (continued)
inhaling cool air for combustion is far better for maintaining max HP than doing so with
hot air.
Update 12/26/06: Drilling holes in the front crossmember can be a challenge; there’s no
doubt about that. To do this, you might want to get ahold of a right angle drill adapter. I
bought an inexpensive one (about $13) and it did the job, but the most important advice I
can give is to use new drills. A punch is mandatory to create a divot that keeps the drill
bit from wandering. Start with a center drill if possible (if not, start with a smaller
diameter drill and work your way up to the right size) A # 12 x ½-inch sheetmetal screw
is the largest diameter sheetmetal screw that’ll fit through the Watts filter bracket holes.
The easiest way to make sure both holes line up with the bracket holes is to drill the first
hole, mount the bracket, mark the outline of the second hole in the bracket, remove the
bracket and drill the remaining hole. You can also use a #10 sheetmetal screw to give you
more “error” room.
Now there’s one more thing I should mention – hose type. Do NOT use any old type of
hose for extending the PCV line; use fuel line hose only. I found that there are at least
two types available in automotive supply stores. The better (and more expensive) type
has a blue-colored liner. This is the type I purchased and used about 66 inches of 3/8inch I.D. hose. As I mentioned, though, it IS expensive at about $5.00/foot.
3/8-inch I.D. fuel line
hose
Chances are that either type will work, but make sure that you specify fuel line hose.
Here’re a couple of shots showing the front end mounting setup:
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PCV Line Oil Removal 101 (continued)
Keep the hoses away
from this drive belt! I
used a black tie-wrap to
pull the hoses together.
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PCV Line Oil Removal 101 (continued)
Update: 1/28/07
Measuring pressure drop across an inline filter
A few people who have bought the Watts or other manufacturer’s coalescing filter have
asked me how they can determinine whether the borosilicate glass fiber filter element is
clogged enough so that it is both detrimental to performance of the PCV airline and
subsequently, needs to be replaced. I mentioned previously that a seriously-clogged filter
is unlikely for quite a while unless the engine oil is extra dirty due to negelect (ie: proper
oil change intervals were not followed). However, eventially, any filter will require
changing and after 1000 miles of hard driving, I deceided to check my filter to see what
the pressure drop was across it.
You can do this, yourself, with the following materials:
(1) Dwyer Minihelic II differential pressure gauge, model 5205 Cost = $50
(2) Nylon hose tees for 3/8-inch ID hose
(2) Nylon 3/8-to-1/4-inch ID hose adapters
(2) 6-inch long, ¼-inch ID tubing or hose
(2) 2-inch long, 3/8-inch ID hose
Differentia pressure
(2) 8-inch long, 3/8-inch ID hose
gauge
To PCV valve
Hi-side to intake
manifold
To “Out” side
of filter
¼-3/8 hose
adapter
To “In”
side of
filter
3/8 Tee
Connect everything as shown and start the engine. Here’s what I saw:
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PCV Line Oil Removal 101 (continued)
0-5 PSI Differential pressure gauge
The gauge read 0.60 PSI. What does this mean? Well, not much unless you know what
the gauge reads without the filter plumbed across it. I then bypassed the filter and looked
at the gauge. This time, it read 0.50 PSI. You might ask, “Shouldn’t the gauge read 0 PSI
if there are no restrictions?” Yes, and in this case, the reason why the gauge didn’t read
“0” is that I had negelected to set the pointer on zero before I started. (bang head on wall)
Regardless, the important number in this case is the differential pressure difference
between having the filter connected to the PCV and intake hose, and that of not having
any filter in place. Essentially, the difference in pressure before and after the filter is a
very miniscule 0.10 PSI. Folks, that is really insignificant and means my Watts
coalescing filter is flowing very freely.
Most Coalescing filter manufacturers recommend replacement of the filter element
when the differential pressure between the outlet and inlet ports of the filter reaches 10
PSI (assuming 100 psi line pressure). Because the Watts filter “sees”only 10 psi
(equivalent to the actual 20 inches of mercury vacuum pressure), I may have to see a 1
psi differential pressure before even thinking about changing the filter element.
Remember too, that a serious flow restriction in the PCV line will cause engine idle to
drop noticably.
By the way, here is a zoomed-out shot of my differential pressure measurement setup:
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PCV Line Oil Removal 101 (continued)
Watts filter
Well, that’s all I have for now. I hope you agree that one doesn’t need to spend $130 for
an excellent oil trap. And remember that the cooler the “trap”, the more airborne oil that
will condense and collect in the can.
Best regards,
Dave
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