PCV valve and relationship with rear main seal
 

Will an improperly functioning PCV valve cause oil leak issues at the rear main seal?

This is what I have recently experienced on my 392 Ford Racing motor stroker. There is a breather on one valve cover and a PCV valve on the other cover. A couple of months ago, I replaced the stock PCV valve with a much nicer looking PCV valve/breather with a chromed finish from Spectre performance. The other day while underneath the car, I noticed a very small bead of oil at the bottom of the block plate which was not there months ago. Immediately I figured it was coming from the rear main seal since I did not see evidence of an oil trail from anywhere else. The car is a 2011 build with only 5200 miles on the stock motor. No oil cooler and I use 10W-30 non-synthetic oil.
After reading up on a couple of threads about rear main oil seal leaks, I noticed some references to proper ventilation of the crank case. I then replaced the chromed PCV valve with the original that came with the car (just your standard old school PCV valve with a 90 degree bend). After a couple of days of driving, I now notice that the bottom of the block plate is dry. No more beads of oil.
Could the aftermarket chromed PCV valve have been the issue?

Yes, without a doubt. I had to experiment with mine quite a bit on my truck to get one that worked correctly. Reading articles about them, they all state there is no good way to determine the correct PCV except by using something as close to what the engine had/would have had stock.

Their is an adjustable one made that works nice, but they are rather expensive.

Welcome to the world of positive crankcase
pressure. The adjustable PCV is made
by M/E Wagner and works. It solved
my problem. If your crankcase pressure
is high enough it can also push oil out
the intake gaskets and dipstick tube.

Link to M/E Wagner
Dual Flow Adjustable PCV Valve – M/E Wagner Performance Products

Switching back to the stock PCV valve seems to have solved my oil leak issue. Little did I know that all PCV valves are not created equal and its best to not use aftermarket PCV valves simply because they have a chromed finish and 'look nicer' on the valve cover.

IS it difficult to tune the adjustable PCV valve?

That's why I don't use PCV valves on any engines. A breather in each valve cover is all that's needed.

The Wagner DF-17 is a dual circuit PCV.
One for idle the other for cruise.
Should take no more then about 30 minutes after reading instructions.
You will need a good vacuum gauge to set it up correctly.

Some guys just put a breather on each side of the engine and no PCV.
This works but also then there is NO vacuum to pull combustion contaminants
out of the engine. For racers this is not an issue as the motor is torn down
frequently anyways.

Others with the room to do so, use a belt driven vacuum pump.

It’s odd the PCV system caused an oil leak. Somehow, it must have been too restrictive and the engine blow-by must have been too much for it.

That's what I thought. That's what I tried and had issues. Here's my take on why I needed a PCV system. I used any old parts I could get and maybe I blundered into developing a working system due to luck.

A very long time ago, engines used a road draft tube that pointed down,, was angled back, and cut so that air passing under the car caused a slight vacuum to the crankcase and removed blow-by gasses and moisture. Running with only valve cover vents, and no draft tube or PCV would not cause a vacuum and contaminants would not be removed other than pushed out by blow-by.

When I first built my 428 I gathered parts from all over. A block here, and heads there, a crank from somebody else, etc. Although I bought a couple of complete engines none came with the carb plate for a PCV or any other PCV parts. At the time I thought a PCV was only for emissions and all I did was to install breathers on each valve cover and another at the back end of the intake manifold.

It wasn’t long before I discovered yellow glop dripping out these breathers and after removing a valve cover, all over the inside. As best I could determine, it was water mixed with detergents from the oil. One mechanic said it was from using Quaker State oil, but I switched oil and the same thing kept happening. So I decided to try a PCV system.

I happened to see a PCV valve with one barbed end and the other that would screw into my intake manifold. It was from a 1.5 litre 1990 Honda Civic. That was disconcerting as I couldn’t imagine a PCV valve from such a small engine working, but thought I’d try it.

I screwed it into the manifold and fed it from both valve cover caps as you can see below (the left one, not shown, is the same as the right one, shown):

https://i.imgur.com/5mtbd3U.jpg

The above picture was an experimental attempt and isn’t that cosmetically pleasing, but being lazy I havn’t changed it … yet.

How it works is shown below. I didn’t have and have never installed an oil filler tube, but it would make it easier to add oil, as of now I need to disconnect a hose at one of the oil breather caps so I can rotate the cap off.

Another idea would be to swap the rear breather with one that had a barbed fitting so it could suck fresh air from the filtered air cleaner. However, it does work and there’s no more “yellow glop”.

https://i.imgur.com/lXvxyL0.jpg

This all started out as an experiment, and worked so well I never bothered to change it. After roughly 5 years of cleaning up yellow goop from around the vents and under the valve covers, I installed this system and the goop was completely eliminated. It should be noted that I actually installed this system about 17 years ago and it's been working fine ever since.

For various reasons, I have checked my sparkplugs many times over those years and they all look good with no sign of running lean on those back two right hand cylinders, or any others for that matter. No doubt it’s because at high vacuum (such as idle and light cruising) the PCV valve closes slightly limiting the air fed back into the intake but opens up at low vacuum (high rpms under load) where the flow, though larger, is insignificant compared to the amount of air coming in through the carburetors.

So it appears to me that even a mismatched PCV valve can do the job when one considers the length of time I've had this installed without any problems.

Of course I could be all wrong and that I’m getting away with it as I don’t race my car or otherwise let it scream for extended periods.

PCV valves are hard to get right for a big aftermarket engine. If you have a bone stock 1966 390, then yeah, you can probably get away with throwing a factory replacement PCV valve in and roll. When you're working with a 650 hp 482 FE, then no, it's likely not going to work at all.

You don't know how many phone calls and emails I've fielded over the years where guys are sucking oil into the intake, engine is smoking, etc., because the PCV is bad or incorrectly sized.

You don't need vacuum in an engine, per se, you need venting. An engine will not blow gaskets and seals if it can vent the crankcase.