Gus

Ok I am trying to understand the flow and restrictions in the vent and oil lines from the oil tank to the engine. IF you have a firm understanding of how the system works please correct any assumptions that I have made that are out in left field.
First the larger line at the top of the tank ( yellow) is connected to the intake prior to the butterflies. This makes it a line that is open to normal atmospheric air. But, because it is connected to the intake system it can draw air from the tank bringing oil mist into the intake area.
Second large line from the top of the tank (red) goes to the breather connection on the top of the engine. This allows the engine to breath, but also becomes pressurized and returns some oil to the tank. Can result in positive tank pressure pushing oil out? The upper vent valve on the top of the oil tank should take care of this, to a degree. But, my question here is how much pressure comes out of this breather on top of the engine. On my car i have noticed that below 5000 RPM the pressure seems to be handles by the vacuum line side, but over that the pressure builds up greater and creates a heavy mist or minor oil flow back to the tank.
Is this part of the function of the brether and this return line.
Third line (blue) is a smaller line coming from the tank that is connected directly to the intake manifold after the butterflies which means that it creates a vacuum in the tank as the engine runs drawing an oil mist into the intake manifold. It is noted that while the diameter of the hose is about a half inch, at the tank the hard line has a restriction in it that reduces the size of the opening to less than a millimeter (read small). For those of us running Variorams, (993 and modified 964) I believe that this is why we have the bottom oil seal go bad and the oil leaking on the up engine tin ware.
I have attached several pictures which I hope will make some of this clear. The standard 964 diagram is hard to follow - So, i have also attached the Turbo line diagram which is easier to see how the lines are really linked. And I have added a photo of the top of the oil tank. Color code on the line at the top of the tank. The threaded longer line is the attachment point for the DIP STICK. You can see also the vent valve at top of the tank. Normally it has a curved 'U" shaped hose attached to it as can be seen in some of the diagrams.
I am asking or looking at all this as I am trying to figure out how to reduce the oil accumulation in the intake manifold ( Not good)
One area (if some one knows the answer) is how are all the lines handled inside the oil tank. The vacuum line (blue) must have a one way (out) valve inside the tank. The vent valve on the top of the tank must also be one way out. But what about the other two major lines going into the top of the tank. Is their function somewhat controlled by oil level ??
Feedback appreciated -

Gus

Posted wrong tank pic -

Gus

Trying to get pictures right-

onevoice

There is a cut open 964 tank in this posting, it might be of some help.

http://forums.pelicanparts.com/porsc...bo-flares.html

Most engines have a similar setup, at least in theory. All engines produce some amount of blowby, the vent system is designed to accommodate this without dumping the blowby to the atmosphere. It should, if not excessive, always be drawn into the engine through the line after the throttle butterfly.

The breather on top of the engine will always have a net outward flow of air. The actual pressure should be very small, because of vacuum connection to the intake. Correction: this may not always be true depending on how much the scavenge side of the oil pump can suck. Correction #2. On second thought, the scavenge side of the oil pump has to push oil through the oil filter, so it may not be moving much if any air.

The idea is for the vacuum of the engine to draw filtered air from before the butterflies, through the oil tank, and remove blowby with it. The oil pump also evacuates some air from the engine, because the scavenge side is larger than the pressure side. Note that Item #59 on the u shaped line at the top of the tank is a check valve. Under normal circumstances, this valve is closed so no unfiltered air enters the tank. The system is essentially a closed loop between the crankcase and the intake, before and after the butterfly, ie with vacuum and without vacuum.

onevoice

As to the question of oil in the intake, I don't know if anyone knows. The dipstick has about 3.5" between low and high, so it is a pretty substantial difference of the level of oil in the tank. I guess oil could get sucked into the line, but I doubt it. If liquid oil got sucked into the engine intake, you would think there would be some time when a large puff of blue smoke would come out the exhaust. I have never seen that with mine. The real problem is the low spot in the intake that lets oil pool.

onevoice

Been reading more on this, and found a post on the 993 board where Steve Weiner and Jake Raby both agreed that high oil level in the tank contributed to oil consumption. They certainly are the experts.

The tank is not very well baffled, so I guess it is more likely than I originally thought that oil could get into the vacuum line to the engine. It stands to reason that if oil gets sloshed into the line, it will migrate to the intake because of the airflow.

HiWind

thanks for all the pics Gus and the interpretation w colors etc..

Have you fitted an oil catch can to take the blue and yellow lines off the intake (pre & post butterfly) and just vent to the can (and via a breather on the can to atmos/engine bay (assuming the can is fitted there and not in frunk or under fender or above trans etc...)?

Gus

HiWind - Yes, I now use 2 catch cans - so to say. I left the main line from the engine to the oil tank as it was/is. I added a sealed tank to the line that connects to the intake manifold (after butterflies). This is the line that creates a minor vacuum pressure in the tank. The tank I used is sealed to keep the vacuum pressure, but it allows any oil pulled through the oil tank to be captured in the catch tans and allows the air flow to continue on.
The third line that went to the intake prior to butterflies I ran to a standard catch can that is vented to the out side air.
I tried several configurations, found that the vacuum line from tank to engine is critical. But, this was were the oil was be pulled into the manifold. To control oil added the sealed separator tank. The other vent line also added some oil to intake at higher RPM. So vented it to catch can/air.
Closing off the vacuum line resulted in the oil tank becoming pressurized and pushing oil out of tank - not good.

964George

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HiWind

awesome idea Gus - thanks for being on the ball again! What a great place this is! (C.W.)

So I did the same re the crankcase breather ie left it connected to the tank.

I then took both the pre & post bfly pipes off the intake and ran them to an unbaffled catch can
quite similar to this one but both intakes (in my case) are at the top, drain at bottom and little pipe to show capture level.



I would add pics but 3.8 is newly refreshed top end and away for tune - but this means rings and seats while new are not seated fully yet having only done about 50kms (before I took the car in to be tuned and upgrade the m48 (had elec issue - being sent back to Oz) with an M84 I had (as 9m use)).

So with that in mind i.e. some initial blowby due to new rings etc... I wasn't too surprised to find the round filter type vent on top of the can almost steaming after the engine was warm. The 'steam' (not water obv but the image of a lightly boiling kettle applies) I figured was blow-by and would reduce after a few hundred kms ..... There was no really oily smell on the fumes nor oil in the catch can .....

BUT!!!!!!

I did however notice the oil level indicator not really tying up as it used to with the dipstick and after my longest run of about 10km there was oil being forced up into the filler neck ... so I was pondering what was wrong or potentially wrong and thanks to your insight I recon that is exactly what's happening i.e. the switch of the vacuum line post BFly to catch can means that there is too much pressure in the oil tank - likely causing froth as well as displacing oil from the tank etc... It is interesting/confusing that despite the single catch can being fully vented to atmos there was still pressure build up - maybe the catch can too small or the standard pipes too narrow??

There is also that one way valve on top of the oil tank with the small u shaped hose - surely that should let out some pressure? I haven't check mine - it may be blocked as the tank area is generally pretty filthy thanks to all the leak prone hoses and the stuff that gets behind the wheel arch liner etc.. but I figured that would let off anything too extreme - but that was an assumption which I guess is false!

So i was partly on the track to deciding to try introduce some vacuum back to the oil tank before I read your info .. but was thinking of doing it in a way that wouldn't introduce non-flamables (ie oil) to the compression chamber. I figure it must dampen the ignition to some degree (although I've read it can helps lube the valve/seats etc.. - true?) so it should be avoided. Your approach of using a baffled catch can is very neat as it forces the oil through some kind of membrane and maintains the vacuum likely taking 90% of the fumes out while only getting 10% of the oil that used to goto the chamber.

I watched this the other day - neat product from Ze Jermans - is that the kind of can? Can you suggest one for me to look at please?

Lastly how big a pipe did you run for that vacuum pipe to post bfly intake? The standard 10mm ish ID pipe or a thinner one?

And really lastly for those lurkers who are reading this ... I hope the HP/cleanness gains make up for the work here which I really undertook to
1. remove oil from the intake
2. reduce clutter in the Engine bay (see the thread on engine bay ugly/pretty likely inspired mostly by Rob's efforts at Singer)

... and yes while there are some pipes and clamps and mounting bits removed, having to put 2 cans back in and only really losing one pipe (and not the thickest one at that) .. means the 2nd part of my motivation was pretty much off-base. Luckily for my own rationale, I can cling to the 3 hp I'm winning back and finding a cleaner intake in a year or two when I next remove it for a spruce up

HiWind

I should add that as I've just replaced rings and they wont be seated yet it maybe that this fuming settles down once I get an hour or so of low variation driving done at 2-3k revs.

HiWind

bump for any input on the air/oil seperator on the vacuum line from sump to post butterfly intake

Gus

HiWind - sorry for slow response- major work on car right now- this is the current oil breather hose configuration that I have and it appears to work without back pressure issues.
1. Crankcase breather hose to tank - no change over stock set up.
2. Tank vacuum line (after bfly) ran this line through a closedoil separator tank about size of beer can. It is not vented to the outside air. Is designed to pull reassure from tank but remove any oil before intake manifold.
3. The tank vent line (pre bfly) - I plugged this opening before the butterfly. Then ran the line from the oil tank to a catch can that is vented to the outside air. So this line is open to standard atmospheric pressure.
I have internal fluid level view lines on both catch cans so I can monitor fluid levels.
I have run this system for several DEs with good results. NO oil bow back or leaks from the tank at all.
May not be the solution for all. But I went this route because of the oil that was migrating into the intake. Since I run a Varioram - oil was then leaking out the bottom flap control fitting. Not much or enough to worry about - but enough to oil up the upper engine area.
Hope this helps

HiWind

thanks Gus - that is the same setup I have except I have yet to find the half beer size oil sep can.

I think my issue maybe related to the new rings that aren't yet run in. Also do you know at what pressure the little u shaped pipe vents at on top of the tank? surely that should allow some pressure out?

Gus

HiWind - Try an aluminum drink canister (kind you buy to carry on a run or when you bike)- that is what i used as a catch can - modified to take hose fitting in top and one out- smaller to allow air to escape.
I will try and check the "U" shaped fitting at top of tank - there is a one way valve, not sure which way it works - get back to you