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Here is an interesting/confounding problem that I have encountered. I have reached out to numerous knowledgeable people with no solution as of yet. Everyone has offered helpful info, but the problem persists. Not to drop names, but these people have offered good ideas, but have not solved my specific problems. Chris at Turbokraft, Kevin at UMW and Walt at Competition Engineering. I am interested in any well thought out ideas for what is causing this problem.
These are the problems that I have had since the complete rebuild of a 993 turbo engine. The car runs good. It seems strong and no weird noises or metal in the oil or other issues we can detect. It is a 1997 993 Turbo with 310k on the clock that had a bad engine when I got it. It overheated and had lots of damage due to dog food blocking the cooling fins on the heads and cylinders when it was stored for a winter and then driven to the point of overheating. I dismantled it, overhauled it and cleaned all the parts out carefully including pulling the cooler and oil tank and having them cleaned of all the sludge and debris. I installed a GT3 Crankshaft Pauter Rods a new 996 Turbo oil pump, and a 3.8 piston and cylinder set from Mahle Motorsports. I also put in all new rockers, hydraulic lifters, hydraulic tensioners, rebuilt the heads and had the pitting ground off the camshafts and reworked. I did all the usual rebuild things like clean out the squirters etc. I had Competition Engineering do all the engine machine work and clean out galleries and reinstall plugs etc.
The engine had no leaks except a small one from passenger side chain housing cover. The cover had some pitting and I should have replaced it instead of trying to reseal it. That’s an easy fix and one I should have just replaced with new inititally.
Upon start up, the turbochargers were leaking oil from the center sections. We believe that it was because the units were old and worn and corroded. Even after a rebuild, they leaked. The leaked almost immediately upon start up. We had the turbochargers replaced and they appear to be in good working order currently with new center sections.
The engine warms up nicely until that the point that we believe the thermostat opens and changes the running dynamics of the engine. I have the oil level when warm at about half way on the gauge and the dipstick as well when hot an on a level surfact. It appears that as the thermostat opens, the scavenging pump system begins to falter and gets overrun with oil going into the turbo chargers. It is possible that this happened on the old as everything was coated with thick gunk and may have sealed things up, but I doubt it.
In order to validate that this was what was happening we did some testing. We pulled the scavenge pump line from the aluminum reservoir off the bottom of the turbo chargers and observed the dynamic level for about 20 minutes. Until the thermostat started to open, the scavenging pump easily handled the amount of oil that was going through the turbochargers. It is able to pump about 3 times the oil than is normally introduced by the oil inlet to the turbo when engine is cool. As the oil got hot and the thermostat opened, we noted that the amount of oil in the cup rose and the scaveging pumps seems to stop sucking.
As a prevention I installed 996 oil restrictors on the turbos from Turbokraft. I also talked with Kevin from UMW and he suggested that maybe I was back flow when sitting. I tested for that and we did notice some back flow so I make some lines with check vavles that had a high point like 996 turbo lines and made that system work so there was virtually no back flow. I guess the turbo scavenge pump could have failed and the main oil pump may be able to pull the oil out the turbos, but I doubt that is likely as it would require oil to be pulled by vacuum through the gear complex turned by the layshaft.
I also checked the orientation of the pressure valves in the engine case although I don’t think they could cause this issue. They both were correct in looked in good working order. I am happy to perform any tests or send any pictures that people think will help. I thank you in advance for your ideas and time.
So are you saying you think there’s more flow to the turbos when oil is warm or less oil being scavenged by the scavenge pump? It sounds like the latter. I don’t think we have heard of the scavenge pump failing, but it’s an gear pump and I suppose it would have more difficulty with sucking (vs pushing) hot/thinner oil. There also aren’t many cars we’ve had here with over 300k. FWIW I’d say you need a better working scavenge pump.
To clarify, the flow appears to be the same hot or cold into and out of the turbos. However, when the engine gets hot, it appears that the scavenging pumps not longer remove the oil at the rate they did when the oil was cold or possibly when the oil level in the crankcase is lower. I will determine today if oil flows back out of the scavenging pumps when the oil gets hot and the thermostat opens. It is truly a difficult problem to get my head all the way around and solve the problem.. and its not just me. A number of super sharp people are thinking about it.
Yeah. I bet it is worn, but I inspected it and it looked solid. No pitting etc. The overflowig seems to happen all at once that it stops pumping. That is the strange thing honestly. It seems to be working great, then virtually nothing in a short period of time.
I’ve had similar issues and found a .03 restrictor is required to limit the amount of oil into the turbo. I have high oil pressure at idle when cold 4 bar ish IIRC.
Take the vent line off and cold start when the oil starts running out the vent. Shut it down and try a restrictor
01-13-2019, 01:20 PM
993 Turbo Oil Scavenge Pumps Not Effective
