Okay,
Got one for ya' all.
I have been chasing this issue with oil out my wastegate drain since I got the 81 SD. Frankly it has been pissing me off... recently the problem seemed to have gotten worst whguile on a long road trip so I have been trying to isolate the source because I do not want to pull the head and replace gaskets unless I know it was a cracked head or bad gasket as exhibited by blowby or rebuild a perfectly good turbo to see if it is blowing oil. Anyway you get where I am coming from. So let me tell you what i have done.

I tried to remove the idea of blowby by running the crankcase vent tube under the vehicle because I originally thought this was the source of the excessive amount of oil that was showing up in my air filter housing. I mean the air filter is soaked on one whole side.

So witht eh tube rerouted I ran the car up a good long grade and looked under the air filter cover and there's oil everywhere, including downt he throat of the intake. Hmmm, obviously not coming from the breather hose.

So, thinking that I might have a bad check valve at the bottom of the cyclone drain tube I put the old MityVac on it and it holds the max vacuum I can pull with the MityVac. Seems to be working...

Then I thought maybe I am pulling a sufficient vacuum with the cyclone vent tube in the intake throat that I pulled the vent tube off to see what would happen. In fact, I pulled the whole top off the cyclone just to make sure there was no vacuum created by a venturi effect int he vent tube.
Drove up the hill climb and there is oil again all over the inside of the air filter housing. Blotches splattered here and there. Obvious source is the cyclone drain tube since the cyclone has oil splattered around the sides and puddled in the bottom.

When I noticed this I thought maybe the check valve had broken open or stuck open so I tried to test the check valve again and it appears to be holding like before at max vacuum that my MityVac can pull. Just because I decided to hit the throttle a couple of times and when I did all of a sudden the oil shoots up my MityVac hose. Now remember I had the breather located under teh car so this could not have filled the cyclone drain pipe with oil but it obviously was almost completely full as it shot all the way back up the tube to my MityVac itself.

This leaves me completely and utterly confused/pissed.
BTW - The 3' blowby bypass pipe that I rigged only gets a few drops of oil draining out of the hose after having sat for 10 minutes or so and this is after a hard hill climb so I don't believe this is excessive blowby. The car also never uses oil in normal driving and starts after the first glow cycle at 12 degrees.

So, just for the sake of argument let's rule out blowby then unless it can somehow force all this oil up the cyclone drain tube yet not show any signs of blowing oil all over the place out the breather.
So I come to the big question, why in the H_ll would I get oil blowing up and out of the cyclone drain when the engine is under heavy load?

BTW - these results also rule out what I thought might be a blown turbo seal. There is no way it could shoot oil back up into the air filter housing and neatly hit the cyclone too... This was also one of the considerations I had going into all this though.

Any ideas on this guys?
Could the turbo pressure be leaching into the crankcase and blowing the oil back up the tube? But wouldn't that also manifest itself in some heavy blowby since the crankcase and breather have no restrictions between them?
How about possibly that the cyclone drain is pushed too far into the oil pan and is below the oil level? Then when the pressur ebuilds in the crankcase it creates a pressure increase in the oil pan causing the oil to try to escape the pan via the easiest method (doesn't make sense with the apparently functional check valve but maybe it is weak and wil test with vacuum but the pressures are far greater than I can apply?).
Or how about if the check valve is releasing every time you back off on the throttle a little and the increased crankcase pressure is then shooting the oil up into the cyclone? Could you create enough of a pressure differential by backing off the throttle suddenly?

I'm fishing here and to add to the problem there is no information in any of my manuals about the replacement of the check valve. Not even a mention of it when they talk about the upper oil pan. They talk about the drain tube but not the valve...

Thanks for reading my rant...

__________________
'99 S420 - Mommies
'72 280SE 4.5 - looking to breathe life into it
'84 300SD Grey - Sold
'85 300SD Silver - Sold
'78 Ski Nautique