PCV Modifications and Upper Intake Oil Control
The PCV system is designed to recirculate the internal gases within the engine back into the upper intake
to be burned. In the stock Mustang set-up, fresh air enters in the small tube just before the blade on the
throttle body and enters the passenger side valve cover at the fill tube. This quantity of air has already
been metered by the MAF sensor. The PCV is located at the rear of the lower intake. Vacuum is created
at the PCV and the air is drawn to the upper intake at the other side of the throttle body blade. On
the stock intake, the PCV line is also tied into the upper intake at the bottom on the driver side. Typically,
the line from the vapor canister and PCV line combine as one to enter the upper intake. There should be
a baffle on the underside of the valve cover on the fill tube entry, and a baffle and screen at the PCV
location. When your vehicle experiences excessive blow by, or sometimes with different engine
combinations, the quantity of oil pulled in by the PCV can be significant. Some people will jump to say
your engine needs a rebuild if you experience too much oil getting pulled in. However, there are too
many of us who have experienced the puddling of oil on fresh engines or even just after a simple intake
swap. I have gone from a small amount of oil in my intake to oil literally running down my intake tube
toward my MAF sensor with just an intake swap.
The quick solution is to toss on a few breathers at the fill tube and PCV locations, cap off the throttle body
and valve cover hose ports, and be done with it. Before people cared about emissions, venting
the gases to the atmosphere was the way vehicles were designed. This will stop the oil from being pulled,
however, you will probably experience oil dripping off the filters onto the engine, and the car will no longer
pass emissions (if you live a jurisdiction that cares). I found when I ran my vehicle with this set-up, both
naturally aspirated and supercharged, the engine didn't appear to run as smooth. The engine also
required a change in my fuel tables to really run right. It was also still necessary to clean the oil off the
engine on a regular basis. If you choose the breather route, you need to disconnect the PCV from the
intake. You can't run both systems or you create a vacuum leak at the breather element.
Another route is to install a vacuum pump on the engine. Expect to experiment on your own, as there
are no simple kits to install it on the car. This works great for a race car, but it's not the best for a street
car. It is not emissions legal, and over time, the pumps need to be rebuilt and cleaned.
To try to keep the PCV in-tact, I've tried several ideas that others have posted in the Mustang
forums. These included the use of different PCV valves, a needle valve to reduce the vacuum pull,
and installing an oil/air separator. None the these have worked acceptably to me, but I know
some have had luck with these modifications. If you are using a supercharger, make sure you
have a one way valve installed in the PCV line to the intake. This will help prevent the engine
from being pressurized under boost conditions (photos below).
My latest endeavor has been to add an additional line from the
driver side valve cover. So far, this modification with an oil/air
separator has been the best attempt to control the oil issue.
After driving about 500 miles, I'm getting about a teaspoon of
oil collected in the separator. At this rate, draining it during oil
change intervals is possible and acceptable. Upon removing my
upper intake, you can see that a very small amount of oil mist will
still make it in. However, this is a dramatic change from the other
set-ups where I would have oil puddling in and dripping from the
The following modifications are what I've done to make this finally work:
removed. With the larger roller rockers it's necessary to remove the stock baffle. You
- Install a baffle under the fill tube on the passenger side valve cover if it's been
need to fabricate your own making sure it will clear the roller rockers. (Using Play Dough
and the valve cover / gasket in place, make sure you have enough clearance throughout
the rockers full motion with the valve cover on. Rotate the crank by hand to feel for any
binding). I designed my baffle to fit inside the old baffle support beams with the primary
vent/fill area opening toward the end (front of the car) of the valve cover. Make sure it
doesn't fit so tight against the hole that it restricts the air flow. In one of my earlier tests,
I was able to firmly blow into the oil fill tube and notice a restriction.
I made the baffle out of two small thin pieces of sheet metal. The
first is an "L" bracket attached to the fill tube. The second piece is relatively flat, angled
down and fitted tight at the support beams, and then curved downward near the end of the
valve cover. The plate on the left is an older version, but very similar to my current piece.
The new piece, pictured to the right, extends a little further toward the end of the valve cover
and doesn't have those slits. The two metal plates were riveted together
and then to the fill tube. If you do this, make sure you pinch over the head
of the pulling nail in case it ever decided to get loose. I figured this was
better than epoxy and possibly having the entire baffle bouncing off the rocker if it came loose.
After looking at numerous epoxies at the hardware stores I began not to trust any of them.
Some would say they were good with aluminum, but only to certain temperatures, and others
weren't designed for oil or wet conditions. I couldn't find a product locally that met my
requirements, but it doesn't mean that it doesn't exist. Use a touch of silicone on the fill tube
rivets to prevent any possible oil seepage.
installation of a baffle. There is ample room at the ends of the valve
- On the stock driver side valve cover, I tapped a small hole into the upper rear side. If you have an
aftermarket valve cover, there may already be provisions for a second PCV valve. Just make sure
that baffles are installed. I tapped into the rear of the valve cover because I figured under hard
acceleration there would be little to no vacuum pull where my fitting was. Under hard
deceleration, oil would be thrown to the front of the valve cover at a time when vacuum would be
at its greatest. Though some suggest you install it at the front to try to get vacuum pull at both
the front and rear of the engine. The rear location also facilitated the
cover to play a little without any worry of interference with a rocker
arm. I fabricated a baffle that would be welded in place and shield
the fitting almost completely. The notch in the baffle is for the end
head stud. With head bolts it may not be needed. The baffle sits
inward about 1/8" higher than flush with the bottom of the valve cover. Expect that you
may need to repaint the valve covers after welding. The fitting I used was a simple
90 deg, 3/8" hose end with a 1/4" NPT threaded end.
I didn't use this hole as my PCV mount because of the lack of an
- While I had the valve cover off, I also decided to make a dedicated oil filler hole. (With the
baffle installed on the passenger side valve cover it's difficult to pour in fluids at a normal
pace). The new hole is 1" in diameter with a standard rubber PCV valve cover grommet.
The location of the hole is shown in the drawing / photo and is close to being centered over
the first roller rocker mounting stud. I used a 90 deg PCV connector with a 5/8" heater
hose cap to use as my cap for the hole so I can pull it out easier.
easily installed baffle. The plug is easy to get to, and pouring in
oil is now a 2 minute vs 20 minute job. All of the parts can be
found in the Help or PCV section of Advanced Auto, Pep Boys, etc. You could use this
hole with one of the larger (breather size) push in PCV's, but the hole diameter for those
is slightly larger (I think 1.25" diameter). Some of them come with there own grommet,
and you can even find the larger push in PCV's with built in baffles. So if you wanted to try
one of these PCV's first before the rear fitting as above, thats always a possibility.
I have a Moroso oil/air separator that allows me to relocate a PCV to the top of it or use
- Now, this is where you'll need a little creativity to see what you need for your set-up.
the breather that came with it. Now... You're defeating the purpose of the PCV system if
you have one PCV hooked up while the other is pulling straight from the other hole. So if
you run this system use two PCV"s.
You have 2 options at this point to hook up the 2nd PCV:
1) You can hit the hardware store and attempt to find (I couldn't) a 90 deg, 3/4" or 5/8" hose barb fitting with a
threaded end of about 5/8" for an optional valve cover fitting in place of the one pictured. Then hook the
hose barb to the PCV with ease for your second line.
2) A 3/8" hose will fit snug inside a 5/8" hose. The PCV grommet side fits snug inside a 5/8" hose.
The PCV uses a 3/8" hose to pull vacuum from the top of it. So follow along.... From the 90 deg, 3/8" hose
fitting on the rear of the driver side valve cover; attach a short piece of 3/8" hose, then slip a 5/8" hose
over the end of the 3/8" hose and install the PCV into the other end of the 5/8" hose. From the other PCV
end, you are now back to a 3/8" hose fitting. Join the two PCV hoses (valve cover & lower intake) using a 3/8",
" T " coupler and run the other end to the proper upper intake location for the PCV vacuum source.
If you have an oil separator, connect the separator between the intake vacuum source
and the two connected PCV's. On the Moroso can in the picture, the PCV is gutted and
merely used as a hose connection. The Home Depot air compressor separators use 3/8"
fittings and hoses throughout.
a check valve in-line with the PCV to prevent the crankcase from
- If you have a supercharger, you also need to consider running
being pressurized. If your engine is naturally aspirated, it's not
a real big deal. Bowling Green Customs makes a nice valve
that everyone seems to use and is satisfied with ($20).
the throttle body to the passenger side valve cover fill tube nipple. This is still your
- If your running a naturally aspirated engine, keep the hose in place that runs from
fresh air intake for the engine.
best to tap into the pipe after the MAF and before the supercharger inlet to keep all the air metered. Don't
- For those with superchargers, don't forget to remove the vacuum line off the throttle body and cap off the
throttle body nipple and valve cover fill tube nipple. This would cause built up pressure in the engine if it
remained. You should follow the manufactures instructions for re-routing the fresh air line.
- If you have a Power Pipe, run the fresh air vacuum line from the valve cover nipple to the Power Pipe. It's
forget to add a filter in the line to help prevent particles from entering the supercharger.
Again, this is what has finally worked for me. Hopefully, if you choose to do this, it will work for you. If it does or
doesn't, please let me know and I'll try to post a tally of whether it's working for people or not.