Background Info on the PCV System
The PCV is an emissions device that allows the pressure and corrosive gasses in the crankcase to vent, without venting these harmful gasses to the environment. The directional valve is in place to prevent a backfire from spreading to the crankcase. In the event of a backfire into the intake manifold, the PCV is supposed to seal shut, preventing the flame front from traveling into the crankcase. Without this directional valve in place (and fully functional) a backfire could also cause a crankcase explosion.
All motors will experience some degree of Blowby. Even a freshly rebuilt motor can experience between 5-10% Blowby, as checked with a Leakdown test. (Blowby is not the only source of crankcase pressure however. Due to the reciprocation of the pistons there will be a build up of pressure due to the air not being able to flow as fast as the pistons are moving in the higher RPMs) Blowby of combustion gasses introduces fuel and other combustion by products into the crankcase. Raw fuel, moisture, and various acidic materials will all contaminate the engine oil. Moisture can also enter the crankcase due to condensation overnight.
The good news is that most of these contaminants are highly volatile, meaning they will vaporize at relatively low temps; around 200F. Once these contaminants and moisture have volatized though, they must be purged from the crankcase. This is where a crankcase ventilation system comes in.
In the old days the crankcase was vented to the atmosphere via a hose that ran under the car or into the exhaust. The downside to this is that these volatile materials were being introduced to the atmosphere, increasing environmental damage. Now a Positive Crankcase Ventilation system is in use. In a positive venting system the crankcase contaminants are purged into the intake manifold so that they can be burned in the normal combustion process. This is very effective at reducing the amount of unburned HCs that are released to the atmosphere.Troubleshooting Your Oil Control Issues
The first step is to find out where the oil is coming from.
Pull the Throttle Body/Valve Cover hose from the TB. If it is wet with oil then this is an entry point. The normal causes of this are excess Blowby (which needs to be ruled out with a compression test), or the VC baffle has been removed for rocker clearance. Just looking down the oil filler neck should reveal if the baffle is in place. If you see rockers, then it is time to get creative and fabricate a baffle. If there is no baffle but the TB/VC hose is bone dry then you may be able to get away without using a baffle.
Next pull the PCV hose. Again if it is wet with oil, this is an entry route. A quick fix for this is a separator from Steeda, Home Depot, or Lowes. For about $25 (The Steeda unit will be more expensive) for the separator and fittings you will be able to remove most of the oil before it gets to the intake.
Also, you need to verify that the PCV screen is in place. This often forgotten part is located underneath the PCV in the back of the intake, and helps remove oil mist from the crankcase gasses.Contributed by tmoss...I have seen a BUNCH of intakes (100s) and you can tell the lower intakes that were on cars whose PCV screen had been blocked - they have a very thick coat of grime on the bottom of the lower intake. You know the heads had a nice thick coat below the rockers too as the blow-by had no where to go. When you put the intake in a solvent tank and wash it, it does not cut all the crud off - reason? - the blowby gasses will not come off with safety solvent. why, I don't know.
Do your self a BIG favor and install a PCV screen once a year.
If a compression test comes back normal, and the above mentioned lines are dry, then the valve guides are suspect.The PCV Problem
Many of the Fox Body Mustangs seem to have serious issues with oil consumption through the PCV or Throttle Body/Valve Cover line. There are 3 main causes of this problem.
1. Excessive Blowby
2. Removing the Valve Cover Baffle at the oil filler neck
3. Removing the Baffle and/or the PCV Screen on the lower intake
However, in some head/cam/intake (and possibly stroker) combinations the problem can persist.
Sometimes a small oil/air separator can be used to help filter out the oil before it gets to the intake manifold. Most who run this setup will remove the small plastic filter, as it tends to plug up and restrict airflow. An oil/air separator is a band-aid solution though, and should not be considered permanent. The goal should be to completely eliminate the flow of oil from the crankcase.Theory
The problem seems to be that the stock PCV line does not flow enough volume to allow adequate ventilation in modified motors. The lack of volume flow creates a build up of pressure in the crankcase which forces crankcase gasses through the PCV at higher velocities. With the added velocity the crankcase gasses are able to pick up more oil vapor; carrying it into the intake manifold.
Yet another issue is that the stock single PCV system can create rather long flow paths for pressure to vent. For example gasses in the front of the crankcase would have to flow to the back of the block to exit through the stock PCV. The result of a long flow path is that it will take longer to purge the crankcase pressure.Solution
The solution is to allow a greater volume of gasses to vent from the crankcase, at lower velocities. This can be done with a larger ID PCV hose and PCV, or by adding a second PCV line. Since larger ID PCV valves can be hard to find the easiest solution should be to add a second PCV line to the drivers side valve cover.
The stock drivers’ side valve cover can be replaced with any valve cover that has an oil filler/breather hole. What valve cover is used does not matter, so long as there is a way to mount a PCV valve to the valve cover. A stock passenger side valve cover installed on the drivers’ side would work well, or many of the aftermarket valve covers have holes intended for mounting breather caps.
The hose from your new PCV should flow either directly to the intake manifold (parallel to the stock hose), or merge with the stock hose. An air compressor oil/air separator can still be used to filter out any oil that does get out of the crankcase. However, if the system is setup right and the motor is healthy, there should be very little oil accumulation in the separator if any at all.Secondary Benefits
The increase in the volume of air that can flow out of the crankcase means lower accumulations of harmful Blowby gasses and moisture. Also, lower crankcase pressures will allow greater efficiency and power (although this affect is probably minimal on a street car).More Notes on Installation
1. It may be better to install the drivers side valve cover PCV toward the front of the motor. This will allow a shorter path for gasses that are trapped in the front of the crankcase.
2. It may not be a good idea to install a third PCV on the aft side of the passenger side valve cover, as this could allow fresh air from the TB/VC hose to vent directly out that PCV. This would result in no fresh air hitting the crankcase, and a greater accumulation of harmful crankcase gasses and moisture.Extra Notes
From what I have seen, the oil accumulation in the intake will be greatest when the car is left to idle for some time (stuck in traffic or idling in the driveway), and then with some rpm the oil is picked up and thrown into the combustion chamber. If you live in a humid part of the country, or see a fair amount of condensation on the ground in the morning, then you will most likely notice some moisture in the separator, resulting in the easily recognized brown milkshake appearance of the oil in the separator. This is fairly normal, as overnight condensation will form on the inside of the engine block. Once the oil gets up to temperature, this moisture boils off, and collects in the separator.
The Ford 302 Cobra lower intake has seemed to be the cause of PCV issues. Ford has now revised the lifter valley baffle in order to reduce PCV oil consumption. The new baffle is much larger spanning nearly the entire underside of the intake. The part number is F6TZ-6L678-AA. Others have reported that Ford covers the cost of the baffle, and that shipping is all that the customer needs to pay. The Ford Tech line number is (516) 468-1356. References:http://www.steeda.com/products/steeda_oil_separator.php
Home Depot - www.homedepot.com
Fram PCV Screen - # BA8113
NAPA PCV Screen - # 6978
Napa PCV - # MPF39203 / CRB29203
Fram PCV - # FV198
Purolator PCV- # PV98C
Borg Warner PCV- # PCV203http://www.fordracingparts.com/home/home.asp