Of the many posts on NLOC forum regarding the source of the oil in the intake plenum, I have been informed that the rear most hose(pass side ) that leads from under the intercooler( rear manifold) has been a source of oil and not the pcv valve as much as everyone has thought.Under boost, this hose creates pressure and at idle it has vacuum.. My question is where is this oil coming from.Why is it present below the intake???

 

I speculated that hose to be troublesome a while back as well, but upon furthur inspection, the fitting that hose attaches to on the lower intake has a very tiny orifice in it, and there is not enough vacuum created by that line to suck oil. I found this when I was looking at the setup on a stand motor one day, thinking that that hose was venting boost back into the upper intake, then I looked into it more and found the small orifice. Oh, and disconnecting that hose completely, cause some funky decel noises .

 

Yes, but when you manually throttle into boost , that hose becomes a pressure hose..feeding the already strong suction from the t.B. spacer. There is oil being pulled through this hose.How I know this is one of my friends who had the PCV valve disconnected from the "tri-hose" set up, placed an oil sucker tube(commercial variety) into the orifice and was able to pull out oil at least once a day for a week or so.this is a small tube.My question still remains: Why is there oil down there to begin with?The area below the aftercooler is supposed to be free of oil! So what gives?

 

The oil that gets injested into the blower and upper intake through the valve covers, simply goes down past the intercooler into the lower intake.

 

In my last post I mentioned that he disconnected the pcv valve and he even changed the oil after doing so.The oil he then sucked out of the rear tube was fresh oil! So its like the oil is coming from some where else.Truck is tight and a strong runner.

 

Well, the only places oil can get into the intake, is the tube from the drivers side valve cover or the tube from the pass side valve cover. There is no source of oil anywhere in the lower intake. Oil in the lower intake has to be coming from one of the two hoses from the valve covers, through the blower, and into the lower intake. If he's blocked off the pass side, then it's got to be coming from the drivers side tube. Even with the PCV hooked up, the PCV closes off under boost, so any pressure that hose from the rear of the intake makes through the orifice, simply goes back into the upper plenum before the blower. If it's actually blowing oil through that hose, it's oil that's already made it's way to the lower intake, and is simply being recirculated back into the upper, in a big cycle.

 

Makes sense.I told him that as well, though he seems to think it may be pulling past the rings. That seems too unlikely to me.

 

Even if it were pulling past the rings, it wouldn't end up in the lower intake.