930 Oil Drip Tank Fills When Engine Is Off -->Causes smoking

TurboBert · 11:10 AM

I think that the lack of a vent in the turbo drip tank in aftermarket headers (like B&B or GHL) can cause smoking on a startup following a drive. Has anyone come to the same conclusion?

I installed aftermarket headers without a vent and I'm now getting a lot of blue smoke whenever I start up after its been sitting. I think the vent-less configuration lets oil flow without issue, but when the engine is turned off, a vacuum is created that pulls oil from the engine into the turbo. The excess oil stays there until you restart the car, and then it’s burned off.

Here are some tests that I’ve done
1. Checked to ensure scavenge pump is working and oil is flowing when engine is running. I disconnected the oil tube at the drip tank and connected a short tube to the tank nipple to let oil flow into a clean glass pitcher. I placed the scavenge pump intake oil line into the same pitcher (see picture). I started the car, revved it quite a bit for a while and the oil level in the pitcher stayed constant at the level of the scavenge pump intake – as expected. Conclusion: Oil circuit works correctly.

2. Ensured turbo seals are not failing. After a run, I thoroughly drained the oil from the drip tank and turbo. I restarted the car and there was no smoke, not even during a spirited run. I let it sit and then restarted the car – I got huge billows of grey smoke for an extended time. Conclusion: Turbo seals are fine (otherwise it would smoke during all runs) and teh turbo is filling with oil with the engine off.

I've heard that the ball bearing in the oil feed line circuit is suppose to act as a check valve to keep this from happening - can anyone confirm this?

TurboBert · 03-05-2005, 02:23 PM

Problem Solved:

Sure enouigh, the 9mm steel ball in the oil feed line (at pressure switch) was missing . Once I installed one, the smoking stopped.

It's interesting that the stock setup did not smoke with the ball missing. Since the volumes of the stock and custom drip tanks are about the same, I figure the oil must have been backing up in the stock vent tube. This was just enough extra volume to keep it from backing up into the turbo.

Note: If you don't want to wait to special order the 9mm ball, Lowes Hardware sells a 3/8 inch steel ball bearing - works great and allows sufficient oil flow (3/8inch=9.52mm).

Brian Lockwood · 03-07-2005, 01:55 AM

Hi, I have the same problem with my 2.7 after-market turbo. It only appeared after I had work on the turbo done. Could it be that the ball bearing was misplaced or not there. I have no knowledge of the bearing in the oil line, could you pls describe it with one of your excellent drawings so I can find it on my car. A part description would really help. Like you I have been pondering the problem for months. Thanks from down under.Brian

TurboBert · 03:53 PM

Yes, you should check it. I responded to your other post, but for the record the ball bearing is located under the pressure switch which is located in the back of the engine bay behind the air cleaner (#47) in the picture below. You'll need a magnet to pull the ball out of the housing.

Installing the 3/8 inch ball bearing (9.5mm) helped quite a bit, but I found that oil would still backflow into the turbo on occasion - especially after a hard run. To fix this, I installed a 7/16 inch (11.1mm) bearing. I verified that I'm getting plenty of oil flow so I'm confident I'm not going to wipe my bearings (see oil stream in image below).

Edit: I suspect that the new cam oil restrictors I installed during a chain tensioner upgrade may have exacerbated this. The added oil pressure would increase flow, so at engine shutoff it may have been enough to overfill the drip tank and back it up into the vent tube.

blichjr · blichjr's Garage

I FINALLY figured out what was causing my excessive smoking issue on my 89 930. It would literally blow gobs of oil out of the exhaust on cold start. I would estimate 3-4 oz easily. Massive smoke screen for 15 min until it all burned out of the exhaust. Gobs of oil in the intake system as well. Disassembled the turbo scavenge pump and all seemed normal - no excessive wear. Replaced the seals for good measure. During an experiment like Steve did above everything seemed normal. Engine off.
Went in the house to grab a sandwich and when I came back out the bucket was filled with about 20 oz of oil! Note: I'm using stock turbo oil tank.

I repeated the test and verified that it did it again. Repeated again and this time I used a vise grip to pinch off the turbo scavenge pump return hose where it goes back into bottom of the remote oil tank (immediately after I turned the engine off). The bucket did NOT fill this time. Repeated a couple more times each way and that was definitely the issue. The static oil pressure from the oil tank was pushing oil backwards through the oil pump and overfilling the turbo drain tank over a period of several days. All the oil backed up through the turbo bearings and into the exhaust and intake sides. When the engine fired up all this oil would blow into the exhaust and intake system.

Fix was simple - I ordered a check valve from McMaster.com (couldn't find one on Pelican unfortunately) and installed it in the hose going from the turbo scavenge pump outlet into the bottom of the remote oil tank. Be mindful of the direction - the flow arrow needs to point to the oil tank, not the pump. Problem fixed! It took several runs to get all the oil burned out of the exhaust and sucked out of the intake.

Hope this helps!

John