Well the car sounded funny when my bride pulled it in today and low and behold we had oil coming out of the oil fill cap . I also put a vent tube near the cap but the pressure was to great. I popped the nipple out of the oil/pcv trap and no pressure could be felt. So looks like maybe tomorrow or wednesday I'll be pulling the oil trap assembly. I just did this about 150K miles ago. I do have a new trap that I bough a while back so I'll be installing that. I do recall I did replace it without removing the manifold and maybe a good time to clean the throttle body. Just a little more fun but the real PITA is gonna be hosing down the block in 30* weather.

 

"Only" 150K miles ago? Do you mean 150 miles ago? Either doesn't sound right. How can you put a vent tube near the cap? Popping the nipple out of the PCV trap would be blowing out if the system is plugged, no? I must be missing something...

 

Car has 375,000 miles on it and I last changed the PCV trap assembly at 150,000 miles. At that time I bough another cam cover and drilled a 1/2 " hole below the oil fill cap and routed a hose to a catch can. Just to re-leave pressure in the head. So the PCV nipple is clear and if you put your finger over the rubber hose (remove the nipple) with the engine running there is no pressure there . Also the rubber gasket under the oil fill cap is now leaking so oil is spitting out and down the side of the block. The last time this happened I replaced the PCV oil trap plastic box. I'll be doing that in the next few days along with cleaning the throttle body and then my 5K oil change.

 

next time you do the PCV system, you should rod out all the block ports when you have the tubing off, then drop the oil pan and clean from the bottom up to get as much of the gunk out of the lower end. Some people also advocate doing a Seafoam treatment prior to doing the PCV / trap to help (I can't speak to how effective that is).

 

 

Well I pulled and replaced the PCV plastic box but it appeared to be clear. Looked at the flame trap and it was clear . So the question I am trying to sort out is why there is so much pressure (blow by) in the cam cover which blows oil out of the fill cap. I also removed the PCV hose plugged into the intake plastic hose and there seems to be no change in the cam cover pressure. At this point I am looking for a solution to vent the cam cover to avoid oil being blown over the side of the engine. This PCV system appears to be pretty simple and I would have thought if I pull the PCV hose off of the intake tube the cam cover pressure would be reduced . I'll need to do a compression check as the only other way there is pressure would be leaking through the valves or maybe a head gasket. Anyone got any thoughts about this. Maybe I look for an engine rebuilder next year.

 

if the hoses are clear, then it suggests the clog is inside the block. A pretty common problem for 850s so I wouldn't be surprised if you have the same. Check out Tony1963's sticky post on the S60 board on crankcase serving for some insights.

 

Interesting as I stuck a screw driver down the return hold before I replaced the PCV trap box. Seemed clear.

 

The system on my 89 740 seems pretty simple if I am understanding how it works. There are 2 holes in the block where one is a vent and one is an oil return. The blow by pressure in the oil pan exits into the larger hole and into the plastic PCV box where the oil is separated out from the vapor. At the flame arrestor nipple there is a small vacuum line which goes into the intake manifold. This is to help in exiting the fumes. Also at the nipple is a large hose that routes to the large plastic intake hose upstream of the throttle body. These fumes get sucked into the intake system and burned in the cylinders. So this would make this a closed system. The question is how does this pressure get into the cam cover because the intake runners are under the valves. One way would be if the valve guides were leaking but is there any other reason for there to be pressure in the cam cover. Another question is if you remove the large PCV hose that goes into the intake hose would this relieve the cam cover pressure. A more basic question is was there any cam cover pressure when the engine was new.

 

Leaking valve guides seem logical. With the miles you have, you may want to do a valve job; total rebuild may not be needed--once you have the head off you can be sure either way.

 

It is obvious I must be obsessed with this but just trying to picture the cause. This morning I cut the old plastic PCV box in half at the seam . Nothing obvious as it just has a few baffles inside where the liquid oil runs to the hole going into the oil pan and the vapor going out of the top into the flame arrestor nipple. Pretty simple and is basically a cheap oil catch can. With winter here in the NE I'll wait until spring and then decide when I'll want to open it up and check the block. For now I've got a patch in place by dumping the cam cover pressure into a separate catch can. Also I've double gasket-ed the oil cap so the pressure goes into the catch can. Just a rube goldberg set up but it keeps the oil off of the engine and preserves the seals. FOr now I'll just move forward. Oh if anyone wants me to post a picture of the OEM oil PCV tank cut in half I'll do it before I throw it out.

 

"if anyone wants me to post a picture of the OEM oil PCV tank cut in half I'll do it before I throw it out."

Please post...thank you.

 

Here is a picture but not to much to see. Just an open box once you cut it in half.

The top piece in the picture is the bottom of the box where the liquid oil drains back into the oil pan. The bottom of the picture is the top of the box which attaches to the hose with the flame trap in it and the vacuum line as well as the large hose that goes in to the intake . This is for oil vapors . Pretty simple.

 

Nothing wrong with it...

 

doesn't seem clogged at all...
question.. at 375k does the engine burn any oil?

 

Yep it was in normal operating condition. Function was correct.

 

Nope it was OK. The car does not burn any visible oil but does have a rear main seal leak which is not significant. I have changed the oil every 3000 miles the first 5 years of ownership. Bought the car new in 1989. I then started changing oil at 5000 miles which I still do today. I have used 10W-40 since day 1 which was the recommendation. My oil consumption today is about a 1/2 quart between changes. This would be both oil burned and oil leaked.

 

for whatever its worth i have used 10w30 dino oil as per the manual since i had the car. it doesn't use any between changes, but then again it
only has about 210k on it.. no blowby or major leaks sofar..
it may be your engine is simply going through its mid life crisis at 375k !