Turbo Gravity Drain, does it work?

[911st]

My guess to was the turbo tank there to let the turbo drain down after shut off.

Another but lesser thought might be that the pump could at times become a restriction and the tank might help keep the turbo seals from having to deal with as large of a pressue spike.

I hope CopBait will help us out here.

[sjf911]

Originally Posted by 911nut

Yup. I typically have 7 ounces of oil in the catch tank after a good, long shutdown.
If one just runs a line from the turbo to the sump, that oil has to go somewhere. Will it back up into the turbo?

I think coking of oil standing in the bearings and return line on shutdown is the real problem exacerbated by the relatively low position of the turbo in the 930 set up. The best solution seems to be the drip tank which then creates the need for a scavenge pump. I would bet that even with the best technique of avoiding hot shutdown and using high quality synthetic oils, the bearing and shaft seal life of the turbo is still reduced compared to drip tank plus scavenge. It would be an interesting experiment to look at turbine bearing housing oil temperatures under the different parameters of hot/cold shutdown and drip tank versus no drip tank.

[911st]

Is coking more a problem above or below the turbo?

[sjf911]

Originally Posted by 911st

Is coking more a problem above or below the turbo?

I had a friend years ago who owned a turbo re-manufacturing business and he would not warranty his work if you didn't replace the drain tube at the same time. It was his contention that coking frequently caused outflow restriction and premature turbine shaft seal failure and bearing failure. I would assume that outflow obstruction decreases total oil flow, increases oil transit time through the bearings (increased heating), delays draining on shut down increasing coking at the bearings and outflow in a self-reinforcing manner, and increases the pressure gradient across the system stressing the seals.

[Rob 930]

When I first bought my 930, the previous owner had installed a gravity drain system. I restored it to a scavenge pump system during my many modifications. I still have that extended sump, which has about a -8 AN fitting for an oil line that led to it from the turbo. I have no use for it; if anyone is interested in acquiring it, please send me a PM.

[kenikh]

Rob, sent you a PM. Can pick up locally any time.

[patkeefe]

I had a drain to the chain cover, then I ran Ben's setup. Both had problems draining and smoking. I then went to an electric scavenge, which works well.

After thinking about this for a while, I have concluded that since I had a broken oil ring (which, I was unaware of at the time, and forced a new rebuild), that I was obvously running elevated sump pressures, which opposed the gravity drain. I tend to agree with what Ben said, that draining into the sump where you have a relative negative pressure of the scavenge side of the oil pump, that should be the optimal drain point.

[Jim2]

All, I've had my turbo 993 project running for over a year but it's seen little action due to tackling other mods. I'm back to looking at the gravity drain which I believe I'll have to change out for a scavenge pump. When I built this turbo system I placed the turbo as high as possible to promote drainage but after a good romp on the throttle I get a lingering oil smell for the next while, and I've noticed a drop of oil coming off the compressor housing which I presume is a result of oil getting past the ring seal then migrating across the compressor back plate and out the compressor housing seam. The compressor discharge tube is dry and shows no signs of residue.

The oil smoke became evident after getting the car running so I looked into the breather system which is quite different from a 911/930. I had to remove the oil reservoir and install a 1" outlet to replace the twin 3/8" outlets, and I had to go inside the tank to open a 1/2" hole in a baffle leading to the 3/8" vents. Total PITA! I now have breather passages which are at minimum the same size as a 930, and therefore my crankcase pressure (if any) would be similar to a 930.

I've thought about a drip tank like the common aftermarket units but I don't see this being any advantage, as the drip tank will fill and I'll be back to the same drainage issue while under acceleration. The length of the drain tube from the turbo forward to the drain plug is nearly 18", and the elevation from the drain plug to the bottom of the turbo bearing housing is about 6". I see no other option than to scavenge unless you folks can come up with something I'm overlooking.

It's difficult to get a good photo of the drain, but you get the idea, drain tube is about 11/16" ID though including the fitting into the case. Turbonetics single ball bearing turbo has about 50% of the oil flow rating of a conventional T3/T4 journal bearing turbo.

[Rodsrsr]

I've come to the conclusion that its hit or miss....I never got the drain method to work on my 3.2. so I use an electric scavenge pump and even that needs a relay to keep it running for 60-90 seconds after shut down. Little bit of a hassle, but its 100% every time. No smoke ever.

[Tippy]

Mine drains to the cam housing cover and more or less uses the oil pressure to force the return oil back.

This is one of those things I wish I had a solid fix for. I rather not go scavenge pump but that is probably the only 100% sure way to get it to work.........just like the factory intended.

I may try the oil drain plug method and see how that works out.

[proffighter]

Why are you guys trying to avoid the stock solution with the drip tank (aftermarket is fine as well) and the scavenge pump while it's a bullet proof solution without issues?

Mine is working without problems since I have the car over ten years and since about eight years I reduced weight a lot using DIY lines and aftermarket drip tank:

[Tippy]

Mine is a Carerra, hence no pump if you were asking me.

[Rodsrsr]

Mine too.

[proffighter]

Yes I know. Poor asking from my side

I mean why not add the pump like stock 930 Turbo?

[Jim2]

Thanks for input guys, it looks like the writing is on the wall. I have a 930 scavenge pump but was avoiding having to add it.

Roland, my reason to try and go without was to avoid complexity, plumbing, weight etc. Being a 993 platform motor and chassis the installation is more work than the 911/930 installation and I'm at my tolerance limit with this project. Every mod on this project seems to require subsequent mods to adjacent components.

I'll likely go Cole's route and plumb the scavenge return line into the breather cover which will be far more simple than dealing with the oil reservoir again. I need to see if the 993 cam box can accommodate mounting the scavenge pump first, otherwise I'll go electric.

[Tippy]

Yes I know. Poor asking from my side



I mean why not add the pump like stock 930 Turbo?

Cost, weight, complexity, another component to fail.

[sundevil64]

Jim2,

I think most of us feel your pain of one thing leads to 10 others. It can be very frustrating and costly. Hang in there. I sometimes take a break for weeks on end... it's like a relationship. To make it work it takes patience, perseverance, luck, and know when to step away...The reward is worth it.

[Jim2]

John, I too have been taking long breaks between tackling projects on this car, but I just find it frustrating compared to the simplicity of the 911/930 platform where you know what your up against, and can forge ahead and complete each task. I think I'm getting old, my drive is fading. On the other hand I'm building a street/track rat for an old friend from an 86 911 and it's progressing just fine.

[911TT33]

Originally Posted by Rodsrsr

I've come to the conclusion that its hit or miss....I never got the drain method to work on my 3.2. so I use an electric scavenge pump and even that needs a relay to keep it running for 60-90 seconds after shut down. Little bit of a hassle, but its 100% every time. No smoke ever.

Rodsrsr, where are you pumping the turbo oil back into from the electric pump? Care to share some pics?

[Rodsrsr]

Originally Posted by 911TT33

Rodsrsr, where are you pumping the turbo oil back into from the electric pump? Care to share some pics?

On my 3.2, its returned to the oil breather on top of the engine.