OK,

The PCV system in the turbo models is quite an elaborate (Rube Goldbergesque) system. It seems to me that there are a few modifications that we could make to the system to improve its efficiency.

Let me explain my understanding of its purpose/operation and where I think some improvement may be made.

1: The purpose of the PCV system like any PCV system is to provide a small vacuum to the crankcase of the engine to evacuate fumes from combustion gasses that get past the piston rings and from hot crankcase oils. It is designed to use intake vacuum to do this and allow the gasses to be burnt in the engine.

2: On the 850 Turbo there is the "oil trap" or "vent box" attached to the block. This has Three positions open to the crankcase. The top connection and hose that pulls from the valve cover, the uppermost block connection to vent the crankcase and the lower position to return the oil to the sump. This is then vented via a hose to the turbo inlet area via the bayonnet type connector in the inlet hose.

3: This inlet connection also has a vaccum (Manifold vacuum/pressure) routed through it. On some cars (I believe due to a recall/TSB) this is also routed through a metal tube under the plug wire cover to bring heat into it. (something to do with Ice Crystals hitting compressor?) The connector is also heated, I presume to keep the oil fluid in cold weather and cold climates.

Now here is my theory on improvements.

1: I have absolutely no idea what the manifold line really does. I see that it might help provide vacuum to the crankcase at low engine speeds but by the same token would reduce the vacuum on the PCV system under boost. (when cylinder pressures are highest and there is the most blowby or need for PCV).

I would think it best to completely remove the manifold line from the system. Thus allowing the inlet tubes vacuum to act on the PCV system without manifold interferance. The only issue I see with this could be, if the intention of the manifold pressure is to "atomize" the oil in the PCV line and/or act as a "siphon".

2: Some sort of screen or mesh could be put into the oil trap to reduce the amount of oil droplets traveling towards the turbo inlet.

3: Slightly restrict the amount of vacuum applied to the top of the head to increase vacuum to the crankcase.

Any thoughts / comments please....If you think I am nuts let me know also...LOL

 

That might or might not work but the only way to find out for sure is to try it.

 

Tech,

I think I will try it out. I have access to a millibar pressure/vacuumgauge from work. I will plumb it into the PCV line and run a baseline test to see what kind of vacuum/pressure. Then I will remove and plug the Manifold line and retest under similar conditions. I should be able to report back sometime this week.

As far as the other ideas for restricting and trapping the oil I will wait until I can prove an increase in the vacuum. It will require cutting apart an oil trap and filling with some sort of mesh so it will be more involved.

BTW
The reason behind all this is the main seals and cam seals seem to be a common problem in these engines from looking at the posts etc. The more vacuum the less likely the seals are to leak (Up to a point then you start pulling air into the engine) In addition if we can increase the flow through the PCV system we might reduce the common plugging issues.

 

The seals start leaking due to vent system being clogged and excess pressure building up in the engine.

 

Tech,
I was reading this post and I have read several others about the leaking seals. Question: Are you saying that the cause of leaking seals in these engines can be pointed to, in most cases, a clogged vent system? I.E. leaking rear main seal?

My rear main leaks, but I currently am losing about 1/2 quart every 1500 miles or so. Depends if those are around town or highway. Highway I go farther. I have not yet decided to tackle the rear main.

But what I am reading is the PVC system is a culprit. How does one know when to service this system? Any suggestions, comments, is greatly appreciated.

 

Yes most of the seals start leaking due to vent system being clogged. The systems are a pain to check but check all smaller vacuum lines for clogs. Aldo sometimes the big line breaks and messes up the system.

 

Autoxray,

The leak you are describing is a definate candidate for checking the PCV system soon. Assuming you have over 100K miles and the PCV system has not been serviced it is probably due for it. Having done this job a few times as a backyard mechanic (3 x 850 turbos in the family) I can offer this advice.

A: On two of them the Oil Trap was nice and clean the 3rd was a little cruddy
B: The hose going from the top of the head to the oil trap was cracked on one car and very loose at the head on the other.
C: All three had serious build up in the connector to the inlet tube at the turbo.
D: The worst (my wifes 94 with 125K miles when I got it) had 2 breaks in the main tube from oil trap to inlet tube.
E: Vacuum elbows were soft and closing off on all three

I reccomend the following procedure (TECH or JPN weigh in if you disagree) for anyone with this system that hasn't been service in over 30,000 miles.

1: Unless you are extremely picky or do not have a Dealer nearby do not purchase an entire system. The reason I say this is I was able to purchase just the few hoses and tees needed to repair the worst of the systems for about half the price of a complete kit.

2: Plan on changing the oil at the same time and purchase a intake manifold and throttle body gasket ahead of time (you will see why later)

3: Buy and use a decent "10 Minute motor flush" or some "marvel mystery oil" this helps break up some of the sludge. (If you are religous about oil changes and use good detergent or syntheticoils then you can skip this step)

4: Disconnect battery, jack car and drain the oil, remove the filter and let everything drain.

5: Remove the inlet tube from air box to turbo, (be careful of the PCV tubes and the turbo control valve vent tube attached on the underside of inlet tube.

6: Remove Spark plug cover, the throttle body cover, the throttle body to intercooler hoses along with the idle air valve.

7: Disconnect the connections for the Throttle position switch, the EGR temp sensor.

8: Disconnect the vacuum lines on the vacuum tree and the manifold.

9: Bleed off fuel pressure from Schrader valve on right end of fuel rail.

10: Disconnect the fuel inlet and return hoses.

11: Loosen the large compression fitting on the EGR valve until it is free.

12. Remove the intake manifold to head bolts. Give the manifold a "pop" with your palm or a rubber mallet to loosen it.

13. Taking care to not damage the dipstick tube pull the manifold up and out. (you have to remove the PCV hose going to the top of the head)

14. Remove the oil trap (2 bolts I think 10 or 12 MM) and clamps for the upper and lower connections to the block.

15: You can tell by the weight of the oil trap what condition it is in. It is hollow so it should weigh almost nothing. If it weight like 2 pounds or more then it is filled.

16: You can try cleaning a plugged one (I was successful with 2 cans of carb clean and some patience) or you can replace. Check the condition of all the main plastic pipe.

Replace any broken pieces and reassemble, you can replace the clamps with worm clamps or fuel line clamps. (those special "CV" type clamps need a tool and tend to overtighten. Check the holes into the block with a piece of wire to be sure they are clear.

Before putting intake manifold back on remove the EGR valve (8mm) and clean the hole to the manifold and the valve itself. (these are almost always plugge with soot). Also remove the throttle body and clean it and the throttle plate. Again this is ALWAYS dirty.

Reinstall everthing in the reverse order inspecting ALL the vacuum lines and elbows. (these are cheap enough that I just took them ALL off and went to the dealer and bought the replacements.)