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Turbocharger Oil Seal Leakage Explained

Old 02-04-08, 06:16 PM
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Turbocharger Oil Seal Leakage Explained

Even though I don't have a single turbo car at the moment, I understand the frustration that turbo oil seal leakage can cause. Given such, I wanted to take some time to explain how the seals in a turbocharger works and why they sometimes leak oil. The picture below is the cross section of a ball bearing center housing. I labeled the main parts pertinent to oil sealing.



The seals in almost all turbos today are piston ring seals. They look like piston rings that are compressed when they are installed to leave minimal gap between the ends of the rings and around the rings. This forms a torturous path for the oil to prevent leakage into the air passage. Most performance turbos use only a single piston ring on the compressor and turbine sides because they do drag the rotation of the turbo which reduces mechanical efficiency. In applications sensitive to oil leakage for emissions, etc. it is not uncommon for 2 piston rings to be used on both the compressor and turbine sides.

On the compressor side, generally there is some kind of oil splitter which throws oil away from the seal as it is spinning. Because the piston rings and the splitter are dynamic seals, when the turbo is spinning faster, the better the seal operates.

The oil leak is driven by pressure, like any other fluid flow. When the oil pressure inside the center housing of the turbo is higher than the air pressure outside of the seal, the oil wants to travel outside to the air passage. The air that is holding the oil back on the compressor side is the compressor outlet pressure and for the turbine side, it is the turbine inlet pressure. That is because it is the air pressure that is behind the wheel (depends on wheel geometry and air pumping by the wheel too). This is why turbos leak more at idle/low load conditions and leak less when under full load/boost. The picture below is a depiction of the oil leak path.



Common failures of piston rings and sources of turbo oil leakage:
1. Seal collapsing- When the seal collapses from oil coking and heat and no longer provides a positive pressure on the sealing surface.
2. Seal wear- Even though the seals are made of very hard steel, they can wear thin axially and the leak path is now larger.
3. Contact surface wear- If the center housing bore or compressor backplate bore diameter is worn from seal contact and is no longer smooth or round, an oil path is formed.
4. Incorrect piston seating- It is possible to damage the piston ring, sealing surface or just not get a good seat when the turbocharger is assembled.
5. Out of tolerance parts- If the seal bore is oversized or if the piston ring is out of specifications it can create a large leak path.
6. Pressurized crank case- This can cause higher center housing oil pressures.
7. Oil drain kinked or too horizontal- As a rule, the oil drain should not be any more than 15 from vertical so there is no problem with oil drain that can back up the oil similar to #6.

Why oil seal leak is so evident in single, big powered cars:
1. Large turbos on small displacement engines means that turbo speeds are lower than properly matched turbos, therefore, the dynamic seals are not as effective. Furthermore, the air pressures at idle are likely lower on the turbine side with a large turbo.
2. Turbo oil inlet pressures and flow are not closely monitored nor properly restricted. (Should be around 20-30psiG for a ball bearing, a little higher for journal bearing)
3. Insufficient oil return line size- If oil is backing up and not properly draining from too small of a drain line, then the oil pressures become much higher in the center housing which drives more leakage.


I hope this can clear up questions for all of the large single turbo guys with oil seal leak problems.

Kevin

Last edited by CarbonR1; 02-04-08 at 06:34 PM.
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Old 02-04-08, 08:09 PM
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Old 02-05-08, 12:33 AM
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You might want to bring up carbon (compressor) seals, since stock FC's and (I think) stock FD twins use them instead of dynamic seals?


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Old 02-05-08, 06:09 AM
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Old 02-15-08, 11:08 PM
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Funny timing you mention this. I recently tore down a supposed " fresh garrett rebuilt turbo" from ebay. Turbine seal land out of spec, and an out of spec chra, causing a turbine seal leak. Just another reason to stay away from ebay..
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Old 02-17-08, 10:50 AM
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Originally Posted by 1Revvin7 View Post
Funny timing you mention this. I recently tore down a supposed " fresh garrett rebuilt turbo" from ebay. Turbine seal land out of spec, and an out of spec chra, causing a turbine seal leak. Just another reason to stay away from ebay..
Definitely stay away from ebay for turbos. Anybody can take apart a turbo and put it back together but that doesn't mean the turbo is good again (as you pointed out).

I've never worked with carbon face compressor seals but instead of using a torturous path with a piston ring, they are made of carbon for low friction and create a positive seal (makes physical contact to seal). This can be used for applications when compressor pressures are really low (like if you have to mount your compressor stage post throttle body). Unfortunately these seals aren't the best for performance since they have more drag.
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Old 04-11-08, 12:17 PM
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how do u fix a leaking seal on a turbo? do you have to replace the entire turbo or can you just replace the seals. im not very familiar on this stuff but my speed3 has a seal leak that mazda doesnt wanna cover under warranty so im trying to figure out what im gonna do

thanks
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Old 04-13-08, 01:35 AM
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In order to fix a leaking seal on a turbo, the problem first needs to be identified. If can be as easy and unkinking a return line, but if it is the actual turbo, then the turbo needs to be rebuilt. Also, in order to say if you can just replace the seals depends on whether the seal is collapsed and stuck on the shaft wheel or if there is damage to the seal bore. If neither is the case, the seal can just be replaced. I can't comment much on why Mazda wouldn't fix your turbo if it is under warranty.

Originally Posted by SPORTinjected View Post
how do u fix a leaking seal on a turbo? do you have to replace the entire turbo or can you just replace the seals. im not very familiar on this stuff but my speed3 has a seal leak that mazda doesnt wanna cover under warranty so im trying to figure out what im gonna do

thanks
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Old 04-14-08, 09:56 PM
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Originally Posted by SPORTinjected View Post
how do u fix a leaking seal on a turbo? do you have to replace the entire turbo or can you just replace the seals. im not very familiar on this stuff but my speed3 has a seal leak that mazda doesnt wanna cover under warranty so im trying to figure out what im gonna do

thanks
Mazda should cover this and it is a very common problem with the speed 3 and 6 there is something wrong with the design. My dealer has been replacing alot of them but i think they are just going to leak again so you are better off going with an aftermarket turbo kit if they will not cover it to prevent that problem and get some more hp which you will probably want anyway.
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Old 08-30-08, 07:02 PM
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"The oil leak is driven by pressure, like any other fluid flow. When the oil pressure inside the center housing of the turbo is higher than the air pressure outside of the seal, the oil wants to travel outside to the air passage. The air that is holding the oil back on the compressor side is the compressor outlet pressure and for the turbine side, it is the turbine inlet pressure. That is because it is the air pressure that is behind the wheel (depends on wheel geometry and air pumping by the wheel too). This is why turbos leak more at idle/low load conditions and leak less when under full load/boost. The picture below is a depiction of the oil leak path."

I wanted to highlight on this statement above as to have a better understanding on how oil seals work, and also to identify on something I have noticed.

Could I be right in stating that you could create an oil leakage through something as simple as a compressor pipe popping off and continuing to run it in this state for a period of time. As the compressor side of the turbo would lose its capability of pressurizing the turbo from keeping the oil out of the surge path. And in fact would create an almost vacuum effect sucking oil into the compressor path As you have stated this would create higher pressures inside of the center housing than the compressor pressure.

The reason I bring this up is I notice when I pop off a compressor pipe and drive it for a period of time say I'm late for work or something. I notice more oil residue then normal, could this pressure difference be the problem.
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Old 09-01-08, 12:33 PM
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If your compressor outlet pipe was removed and the turbo was run in this condition, it is possible to leak oil a bit more because you are not building as much boost. This problem would go away after you reinstalled the pipe though, and should leave any long term damage to the oil seal.

The main concern with driving like this is that you are no longer loading your compressor wheel, so you are free wheeling it and you can overspeed and damage the turbo this way.

Originally Posted by lopedl View Post
"The oil leak is driven by pressure, like any other fluid flow. When the oil pressure inside the center housing of the turbo is higher than the air pressure outside of the seal, the oil wants to travel outside to the air passage. The air that is holding the oil back on the compressor side is the compressor outlet pressure and for the turbine side, it is the turbine inlet pressure. That is because it is the air pressure that is behind the wheel (depends on wheel geometry and air pumping by the wheel too). This is why turbos leak more at idle/low load conditions and leak less when under full load/boost. The picture below is a depiction of the oil leak path."

I wanted to highlight on this statement above as to have a better understanding on how oil seals work, and also to identify on something I have noticed.

Could I be right in stating that you could create an oil leakage through something as simple as a compressor pipe popping off and continuing to run it in this state for a period of time. As the compressor side of the turbo would lose its capability of pressurizing the turbo from keeping the oil out of the surge path. And in fact would create an almost vacuum effect sucking oil into the compressor path As you have stated this would create higher pressures inside of the center housing than the compressor pressure.

The reason I bring this up is I notice when I pop off a compressor pipe and drive it for a period of time say I'm late for work or something. I notice more oil residue then normal, could this pressure difference be the problem.
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Old 09-01-08, 02:42 PM
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I have sometimes, had to add a small pump in the turbo drain pipe, just to make sure there was no oiling probs. it actually puts a vacuum in the drain to suck any possible oil from going past the seals. HEY! it has worked for me on stubborn projects. gear pumps and gerotor seem to work the best.

Thx Ron
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Old 09-03-08, 10:16 AM
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Good post !
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Old 09-27-08, 11:07 PM
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Originally Posted by ronbros3 View Post
I have sometimes, had to add a small pump in the turbo drain pipe, just to make sure there was no oiling probs. it actually puts a vacuum in the drain to suck any possible oil from going past the seals. HEY! it has worked for me on stubborn projects. gear pumps and gerotor seem to work the best.

Thx Ron

Scavange pump? I was looking into it but they are pricy for a project I have, I might have to bite the bullet .
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Old 09-27-08, 11:39 PM
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I have a bit of a dilemma.

Not my Rx-7 but another project I have.

I installed a single turbo t04e on a mazda Kl03 motor.

In a mission to understand how the oil bearings work, I ran 0 boost temporarily on this project car for a short period of time. The other reason is I haven't got my fuel mods in yet and wanted to test out the install briefly. I tried to do a couple of test runs with one of the compressor pipes off, and it would spray oil out of it but only under load. At idle it will not spray engine oil out the compressor pipe no matter how depressed the throttle is. And it will not smoke from the exhaust in either condition.

Okay, so then I hooked the compressor pipe back inline and removed the wastegate spring off the exhaust path to limit exhaust entering the turbine side which would also lower turbine pressure. The compressor pipe oil spraying was fixed but then the exhaust began to have a slight smoke from oil entering exhaust side.

So from these test what I am coming to understand is you cannot run the turbo without complete pressure from either side (turbine or compressor) otherwise the oil seal will be suseptible to leakage. From what I have read the oil seals require positive pressure from both sides to seal the oil in. Is this right or am I smoking too much green stuff.
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Old 10-03-08, 01:28 PM
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I would avoid running without a compressor outlet pipe attached. This makes your turbo free-wheel which can overspeed your turbo and cause damage.

The compressor side oil seal needs to be able to generate boost in order to seal oil.

The turbine side sealing will also be affected by the wg since it lowers the turbine inlet pressure, but I have not heard of that being the cause of an oil seal leak.

Originally Posted by lopedl View Post
I have a bit of a dilemma.

Not my Rx-7 but another project I have.

I installed a single turbo t04e on a mazda Kl03 motor.

In a mission to understand how the oil bearings work, I ran 0 boost temporarily on this project car for a short period of time. The other reason is I haven't got my fuel mods in yet and wanted to test out the install briefly. I tried to do a couple of test runs with one of the compressor pipes off, and it would spray oil out of it but only under load. At idle it will not spray engine oil out the compressor pipe no matter how depressed the throttle is. And it will not smoke from the exhaust in either condition.

Okay, so then I hooked the compressor pipe back inline and removed the wastegate spring off the exhaust path to limit exhaust entering the turbine side which would also lower turbine pressure. The compressor pipe oil spraying was fixed but then the exhaust began to have a slight smoke from oil entering exhaust side.

So from these test what I am coming to understand is you cannot run the turbo without complete pressure from either side (turbine or compressor) otherwise the oil seal will be suseptible to leakage. From what I have read the oil seals require positive pressure from both sides to seal the oil in. Is this right or am I smoking too much green stuff.
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Old 11-25-08, 10:43 PM
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Old 11-25-08, 10:43 PM
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Hi CarbonR1, I'm the new user here.
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Old 11-25-08, 10:51 PM
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Where did the pictures go? Stickies are important... Too bad.
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Old 11-25-08, 10:55 PM
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Hi CarbonR1,I'm the new user here.I've found your post on the google.
I have been experiencing kind of smoking out issue for a years.Currently,I have 1995 Audi UrS6,the car smoking out when the car is started up and left it idling.
when I swtiched off and on again,on the idle,the car will begin smoke out again.
I have tried to send PM to you but I couldn't because the board's rules required atleast 3 posts here.

Well,Sometimes it smoked out a bit when It has been sitting on the traffic for a period.Currently ,I have 6 KKK K24s on my hand.I'm sure it's from turbo.because the car will smoke more or less on eachs.I have removed the crankcase ventilations valves,breather hoses for cleaned up last sunday,I have finished the valve stem seals 2 years ago,Motor swapping,also done compression test on it.
Some of my K24s ,I noticed some greasy came out from the hotside housing too,
So that's why It's most likely the smoke is from the the turbo.Maybe I have a bad luck on getting a good turbo. The problem,what is the cause to be shorten the turbo's life? I replaced drain line,old one also no pinched,clogged.Too much oil pressure? how is possible? since motor swapping ,I also used the oil pump
from the new motor.But the car is still smoke out from the boths motor.
Regards,
POP
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Old 11-26-08, 10:28 AM
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IL good post

good post
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Old 11-28-08, 10:59 AM
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I removed the pictures, but I will redraw something and post up new pictures sometime soon.

popdemonic-
I recommend that you start by checking shaft play on your turbos. If they have low mileage and have no shaft play, the seals are probably fine and it is likely something with your setup. Blocked oil drain, too light of oil weight, crank-case pressures too high, too high of oil inlet pressure, etc.

It can be difficult to differentiate a problem with your engine or your turbo. I know because I rebuilt my cylinder head once thinking that it was the valve stem seals when it was actually the turbo.

Inspect your turbos first, look for signs of oil leakage around the turbine since most oil from engine problems would likely be burned off already.


Originally Posted by popdemonic View Post
Hi CarbonR1,I'm the new user here.I've found your post on the google.
I have been experiencing kind of smoking out issue for a years.Currently,I have 1995 Audi UrS6,the car smoking out when the car is started up and left it idling.
when I swtiched off and on again,on the idle,the car will begin smoke out again.
I have tried to send PM to you but I couldn't because the board's rules required atleast 3 posts here.

Well,Sometimes it smoked out a bit when It has been sitting on the traffic for a period.Currently ,I have 6 KKK K24s on my hand.I'm sure it's from turbo.because the car will smoke more or less on eachs.I have removed the crankcase ventilations valves,breather hoses for cleaned up last sunday,I have finished the valve stem seals 2 years ago,Motor swapping,also done compression test on it.
Some of my K24s ,I noticed some greasy came out from the hotside housing too,
So that's why It's most likely the smoke is from the the turbo.Maybe I have a bad luck on getting a good turbo. The problem,what is the cause to be shorten the turbo's life? I replaced drain line,old one also no pinched,clogged.Too much oil pressure? how is possible? since motor swapping ,I also used the oil pump
from the new motor.But the car is still smoke out from the boths motor.
Regards,
POP
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Old 11-29-08, 08:39 PM
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Originally Posted by CarbonR1 View Post
I removed the pictures, but I will redraw something and post up new pictures sometime soon.

popdemonic-
I recommend that you start by checking shaft play on your turbos. If they have low mileage and have no shaft play, the seals are probably fine and it is likely something with your setup. Blocked oil drain, too light of oil weight, crank-case pressures too high, too high of oil inlet pressure, etc.

It can be difficult to differentiate a problem with your engine or your turbo. I know because I rebuilt my cylinder head once thinking that it was the valve stem seals when it was actually the turbo.

Inspect your turbos first, look for signs of oil leakage around the turbine since most oil from engine problems would likely be burned off already.

Thanks CarbonR1,I assumed all of my turbos had over 100,000 mile on clock.
I don't know if it's still working fine.I found some of my turbos has minimal
shaft play when I gap on the shaft. I just switched oil weight from 5W-50 to 0W-40.I don't know if this related.What's the oil weight you're running with?Normally,
It's around 87-92 F. Degree in Thailand. My oil drain shoudln't be the problem.
stock one came up with a very big Diameter.only thing I haven't checked yet is
the oil pressure.the Crankcase Breather System,I put all the hoses of and cleaned
up everything.There're 2 valves.one,Regulating valve.another,one way valve.It
will stay shut under boost and blow by when it's under vacuum.If this valve is blow by all the times.It can push much of oil to the intake tract.I replaced it!.
Valve stem seals have been finished last 2 years.When I cold started in the morning,There's no puff of smoke out.I need to wait until the engine s warmd up
then it'll be getting to smoke.So I think if the valve stem seals is bad.There's will
be puff of smoke since It has been started up.because the oil in the combusion chamber will be burnt out since that.What 's Idea? I've already taken photos of my turbo shaft and rings.I will shoot you an email soon.
Regards,
POP
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Old 04-11-09, 01:35 PM
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hi a quick one a bought a new holset hx40 for my 24c 6clyinder vw engine conversion as im unsure if i should be useing a oil restrictor as if i rev the rev to approx 4000rpm i can bits of oil coming from the snail part of the turbo //boost hose outlet ,as exhaust is dry ,inlet is dry as well with very minimal play as im unsure what the correct size is ,due to not wanting to damage the turbo bearings ,,,
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Old 08-04-09, 04:08 PM
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good info
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