Yes, they do. Many CAC's can alter pressures so much that they can force failures. Just because you have oil in the can doesn't mean that there is an issue. The super hard rings inside of the EB cars take a LONG time to break in and seat completely. A new car (>~10,000 miles) will have that "issue" occur, because break in has not occurred. If blowby were a real universal issue we would:
a, make a catch can
and
b, use them.
We have never had to install them on any build that we have done here.
I'm not talking about pressure change from the CAC, I'm talking if there's any pressure change from a catch can. I have a stock SHO that I always fill with Shell 93 octane gas, and it has 75k miles. Regardless, I had oil in the CAC that I removed with a pump this winter. This is a common issue and there are several threads on this forum with how to remove the oil. Bottom line is oil inside the CAC that can be measured with the dip stick is NOT normal.
Here's how I understand the issue of oil accumulating in the CAC, so please tell me what's wrong with my understanding. The PCV system has a dirty side with the PCV valve on the rear valve cover. Then there is the clean side of the PCV system on the front valve cover. Under non-boost operation there is a vacuum in the intake that is used to draw crankcase vapors (which contains oil vapor) out the rear valve cover through the one way PCV valve. The air being drawn from the crankcase has to be replaced so air is drawn in from the clean side of the system (the front valve cover). This is simply a tube connected to the air intake tube but behind the filter (air is at ambient pressure). Basically, this works just like every PCV system on almost every other vehicle. With this operation everything works as normal and oil vapors pass into the intake manifold and get burned.
Under boost operation the intake manifold is under pressure. This boost isn't fed into the crankcase because the one way PCV valve prevents this. But what this does is force the PCV valve to be closed until boost is removed or the crankcase pressure gets higher than your boost levels. Either way this would build pressure in the crankcase which is bad for every engine I've ever dealt with. However, there is that tube on the front valve cover that is just a tube connecting the front valve cover to the air intake tubes. That air intake tube is at a pressure of roughly 1 atmosphere (or whatever ambient is at the driving location). So the pressure that's built up in the crankcase is going to vent out through the clean side of the system and into the air intake tubes. This air is then drawn in through the turbos, into the CAC, the oil vapors condenses in the CAC and fall to the bottom. That's my understanding on how the oil gets into the CAC and it makes sense because I can see oil in my intake tubing that appears to start from this area. For my car it's used a lot on trip driving down the interstate. At interstate speed, it's under boost (not sure how much but I can hear the BOV vent when I turn off cruise control) and feeding the oil laden crankcase vapors through the CAC.
What I'm inquiring about doesn't really involve the CAC. I'm wondering if I placed a catch can between the front valve cover and the air intake tubing (the clean side of the PCV system) would that change pressure? Regardless of the catch can or not, the pressure at the air intake tube is still 1 atmosphere. It's a matter of how much pressure the catch can adds if any. What I'm trying to do is keep oil vapors from getting into my intake tubing and I see two options here.
The first cleaner option is to install a catch can on the clean side of the PCV system (on the tube between the front valve cover and the air intake tubing). But I'm trying to find out if this would cause an air restriction and cause extra pressure to build inside the crankcase. I would think it would but you have me second guessing this. My second option is to disconnect the PCV clean side tube from air intake tubing and put on my own filter. This would work with identical pressures of the stock system. Under normal vacuum operation it will still draw air in through the same distance of hose with the same pressure at the open end. The only difference is under boost operation, instead of feeding back into my air intake tubing it would feed back into the open atmosphere. Obviously Ford cannot implement this solution because it's venting oil laden vapors into the atmosphere (as was done in the old days) and emissions regulations don't allow this anymore.
My question is very simple, would adding a catch can on the clean side tube of the PCV system increase pressure? Ideally I would like to catch the oil and dispose of it. But if it's bad for my engine, I'll vent it.
