Supplemental PCV system?

[jblackburn]

What type of hoses are recommended to carry oil ladened gasses? My understanding is the silicon is not recommended as it can deteriorate in the presence of excessive oil.

Ideally, rubber. The problem with that, as I'm sure we all know, is it deteriorates, as does plastic. There is really no "perfect" one, but all of the oil cooler lines, etc. are rubber for that reason, because it handles temperatures and fluid pretty well. Ask Advance auto to show you what they've got on the big spools in the back, and take your pick.

[whoa]

Help me understand this project? A little smoke at idle that can't blow up a balloon does not harm anything, and so it is not a problem, and so it doesn't need to be fixed, and certainly it doesn't need to be fixed by introducing a vacuum leak, which is what widening the existing vacuum line or adding another would do. And I don't see the point of adding additional lines for the crankcase gasses to take from the crankcase to the intake unless the existing opening from the PTC to the fresh air intake is too small, in which case just enlarge it. Is the idea that the breather hoses themselves are too narrow? Of course there will be moisture and some oil vapor in those gases, but I don't see any reason to think that's a problem that needs solving either.

[1997volvo850]

I believe you said this in the other PCV/PCT thread also.

I believe the main issue is that smoke shouldn't be coming out the oil dipstick.

While pressure build up is not a problem with a clean PCT valve the fact that the
gases are not being evacuated seems to indicate some sort of problem. And you
have correctly pointed out that the likely cause of the problem is with valve
seals or rings. Understood. I also understand that fixing the valve seals costs around $1000.

The crankcase is sealed, correct? I read somewhere that the PCV system is really evacuating
gases that have already passed through the air intake metering system. So I'm not sure if
adding a little more vacuum will be harmful.

It is my understanding that vacuum in the air intake hose is minimal at idle. The tiny vacuum
hose to the PCT from the intake is intended to deal with these gases at idle. While I can
increase the opening from the PCT to the air intake hose it seems difficult to modify the
tiny vacuum hose from the intake to the PCT valve.

I expect this connection on the intake is fixed in its vacuum capacity. Thus the idea to
provide an assist to this system.

Since the entire auxiliary system would be sealed I don't see how this provide more of a vacuum
leak than the original PCV system does. Someone else explained the effect of these gases on the
oil. I believe they tended to acidify the oil. I will have to look for it.

[whoa]

I'm following you better now; you're not worried about pressure but about acidic oil from the vapors at idle. There will be a lower concentration of those vapors in the crankcase if the pressure is a little less (which is all you'll get from a properly functioning PCV system in a new engine). In any event, if they exceed the capacity of the vacuum line, the vapors exit out the PTC to the fresh air intake, where there's a very slight vacuum at idle.

What I mean by a vacuum leak is that the PCV vacuum nipple at the intake manifold is a "controlled vacuum source", which has a known/assumed effect on intake manifold vacuum level for fuel management. Your plan is to have more flow of unmetered gases into the intake manifold at idle, which is a vacuum leak. That may make for a lean idle, depending on the amount of the leak. But it will certainly help with lowering the pressure of the crankcase at idle.

Pressure is certainly a problem at load (leaks, seals), and to my way of thinking a much bigger problem than acidic oil, so you want to increase the flow from the crankcase at load. Intake manifold vacuum is low (or, in a turbo, negative, i.e., boost) when the engine is working hardest and producing the most blow-by. So the PCV vacuum flow that you had at idle, even if you've increased it, will be smaller at load (indeed, backwards in a turbo--another risk factor in enlarging the manifold-to-crankcase porting), while the need is greater. Even in a N/A car you won't want to simply make an even larger port to the manifold, because that will mean a huge vacuum leak and vacuum levels in the crankcase well under design at idle, when vacuum is high in the manifold. In both N/As and turbos, though, you get at least a slight vacuum at the fresh air intake, and more vacuum under load, so that's where you want to send the gases, and so you want to have more access for the crankcase gases to the air intake than is given by the little opening in the bottom of the PTC. So you need to open that up (you could run another hose, but that really serves no different function; the hole is the bottleneck, not the hose). Opening that up (or adding more hoses if you like) equalizes the pressure between the air intake and the crankcase, meaning crankcase gases will flow to the air intake under load, when there is vacuum there (and the other way to some degree at idle, when crankcase vacuum will if all goes well be a little greater than the very slight air intake vacuum).

But there's a reason that the PTC hole is small. If you make it big, then the poor little PTC vacuum hose can't affect the level of vacuum in the crankcase at idle---the crankcase pressure would simply equalize to the air intake. So, if you're going to supply vacuum to the crankcase it idle at all, there has to be a balance between the size of the PTC hole and the amount of controlled vacuum (so to speak, the size of the vacuum hose). The goal, I take it, is slightly less than atmospheric pressure in the crankcase at all times. The big question I don't know the answer to is whether there is any hope of doing these at the same time:

1. making the crankcase-to-intake porting big enough to induce vacuum (and hence vent gases) under load
2. making the manifold-to-crankcase porting big enough to induce vacuum (and hence vent gases) at idle
3. not screwing up the manifold vacuum at idle

One plan: put a vacuum/boost gauge on the dipstick tube so you can read it in the car. Take measurements at idle and under load. Do the same at the manifold tree. Enlarge the PTC hole until you are happy with the measurement at the dipstick tube under load. Put a "tee" where the breather hose goes to the PTC, and connect a hose from the manifold tree to it, and find some way (a valve or other way of restricting flow) to adjust the vacuum flow; give it enough vacuum for the desired crankcase pressure at idle, but not more than is compatible with acceptable manifold vacuum. Take measurements again and repeat.

If you can't get acceptable idle crankcase vacuum this way, you might have to monkey with the intake air valve---reduce the supply of air from it and manifold vacuum will go up.

[cn90]

On my 1998 S70 GLT, I will overhaul the entire PCV soon.

But I have read posts that even after a PCV job, people still have smoke coming out of dipstick, filler cap, presumably from high mileage vehicle (150K+) due to excess blow-by combustion.

I am thinking about this mod: bring an extra hose (blue color) to vent from the hose on top of the engine to the elbow before the throttle plate. This is strictly for additional venting of crankcase gas, what do you think?

PS: I borrow this photo from another DIY, so ignore the "A" and "B" labels.

PCVHose.JPG (72.12 KiB) Viewed 708 times