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Thread: Why turbos leak oil into the exhaust - With Pics!

  1. #1
    Moderator Turbo Mopar Staff Vigo's Avatar
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    Why turbos leak oil into the exhaust - With Pics!

    This is intended to help out all of those here who have not (yet..) taken apart one of our turbos and examined it. For those who have, please bear with me if im restating what might seem obvious.

    ..

    Plenty of us have experienced blue smoke coming out the tailpipe as a result of the turbo leaking oil into the exhaust housing and the oil burning in the exhaust. Plenty of turbos have been replaced over the years because of this problem. I myself have replaced entire turbos to get rid of this problem, even when i didnt know for sure that the one i was putting on wouldn't do the exact same thing!

    The natural thought is to blame the problem on a leaking seal on the exhaust side of the turbo. While this is always essentially true, it CAN be a case of oversimplication, and of regarding the symptom as the cause.


    Now, I'm going to go through a basic pictorial explanation of how oil coking can cause your car to push oil out of the turbo and into the exhaust, something that is alluded to but not explicitly explained in the General Turbocharger FAQ in the Knowledge Center:
    http://www.turbo-mopar.com/forums/vb...e&articleid=76

    First, let's get familiar with the basic turbo center section. We need to be familiar with this because it will help understand the orientation/viewpoint of many of the following pictures.

    This is what our stock log- and TII-style Garrett T3 turbos look like with the compressor housing and exhaust housings removed. The flange area which is at the top of the picture is where the oil feed enters the turbo. The flange area at the bottom of the picture is where the oil drains from the turbo into the drainback tube. The hole that we are staring straight into is the coolant return (exit), and on the side that you cant see is the coolant feed (entrance). If this turbo was mounted on a motor, this would be the view when looking at the backside of the motor.



    This is a view of the top of the turbo, where the oil enters the turbo and your oil line/fitting threads in.



    This is a view of the bottom of the turbo, where the oil drains from the turbo and where your oil drainback tube bolts on.


    This is a view of the center section with the shaft and wheels removed and laid out. The view is the same as the 1st picture, with oil feed on top and drain on bottom.


    This is a picture of the turbo shaft and turbine wheel (the exhaust-side wheel). There is a silver sealing ring in the middle of the picture. This is the 'exhaust seal' of the turbo. This is its uncompressed state. The gap in the sealing ring closes when the ring is 'squeezed' into the center section. When it is squeezed, spring tension keeps the sealing ring tight against the part of the center section that it rides inside of.


    This is a view of the exhaust side of the center section, where that shaft and seal go into the center section. You can see a tiny groove in there.. the sealing ring rides just above that groove.



    A slightly different view of the same area. From here, you can see the light gray journal bearing that the shaft spins on, and the darker gray snapring that retains the journal bearing. You can also see some of the oil feed holes in the journal bearing. This is where the oil comes from that leaks out of your turbo and burns in the exhaust. So, in between those oil feed holes and the tiny groove which is where the sealing ring rides, there is not a flat level surface for the oil to just saunter on over to the seal and leak past it. The oil oozing out from between the journal bearing the turbo shaft will fall into the area below the snapring in this picture, which is partially in shadow. Down there in that shadowed area, there is another hole that the oil will run through and drain down into the drainback tube.


    This is a view up into the bottom of the turbo through the oil drain hole. The inside is being illuminated by a flashlight shining in through the area shown in the picture above. As you can see its pretty empty in there, but if the turbo shaft was in the center section you'd see it passing right through the middle of that illuminated area.


    Another view through the same hole, up into the center section, from the bottom. What you're looking at is the backside of the journal bearing from 2 pictures up. You can see the snapring that holds the journal bearing on this side. Oil oozing out from between the journal bearing and the turbo shaft would fall straight down, towards the camera, and drain out.


    I could not get the camera to focus at this angle. What you are seeing here is the same journal bearing as the previous picture, with light shining through it. Directly below it is a sliver of bright light. That light is coming through the hole i mentioned 3 pictures up. This is the only way i could photograph it. So, oil coming out the near side of the journal bearing would fall straight towards the camera. Oil coming out the far side of the journal bearing, which we see 3 pictures up, would fall down to where this smaller hole is, and then drain towards the camera.


    This is a picture of me sticking a tiny pick up through the oil drain hole to get to that tiny hole from the picture above.


    This is a picture from the outside, showing the very tip of that pick poking through the hole.


    So, as you can tell, im spending a lot of time here describing that tiny hole, where it is, and what oil goes through it. Here's why:

    ALL of this carbon came from THAT tiny hole. The hole was blocked COMPLETELY by it. What you're looking at USED to be oil, but it became this carbon mess from sitting in that tiny area after the engine was shut down and just cooking from the heat of the turbo. Essentially, when it just sits there the oil 'heat soaks' to an extreme degree and breaks down into this junk, which then clogs the hole.


    In this picture from the Knowledge Center article i linked to above, you can see an example of the area of a turbo that becomes restricted in the upper right of the cut-away. However, that is not a stock Garrett turbo, and the way that one is laid out would make it much less likely for it to clog up in the same way this Garrett did..



    So, lets look at this picture again. If the little oil return hole down in the shadows is completely blocked, what happens? The oil oozing from around the journal bearing will fill up the entire area between the journal bearing and sealing ring. When oil is draining normally, there is no pressure here, but when this chamber fills up, it will actually pressurize somewhat from the oil pressure feeding the turbo and being forced out of the journal bearings. Now, the sealing ring, like a cam seal or a rear main or lots of other kinds of shaft seals, is not really designed to hold back fluid under much pressure, so it leaks!


    So, what is the moral of the story here? I bet, looking at all the pictures except the last one, that you thought this turbo was pretty damn clean. In reality, if i had tried to rebuild it (with a brand new sealing ring..) and reuse it without removing that carbon buildup, it almost certainly would have leaked oil on the exhaust side in spite of the new seal. So, obviously anyone rebuilding their own turbo should be absolutely certain to make sure that oil drain passage is clean and clear.

    Also, this is some good evidence to support the idea that you should use the most heat-resistant (high quality? Not sure..) oil you can find, and change it on schedule. Common wisdom seems to be that synthetic oils hold up better to extreme heat. Also, if someone were to remove the coolant lines from their stock turbo (i have done this at one point due to some damage on the center section) or have a non-stock turbo setup that does not use water-cooling, it would be a good idea to let the engine idle and pump some cooler oil through the turbo to cool it down, or use a turbo timer, when shutting down the vehicle. I know that's stuff we've all heard before, and its really not the point of this thread to regurgitate it. BUT, for anyone who has never really understood WHY we are all told to consider that, you now can visually SEE why, and what can happen.
    Last edited by Vigo; 07-28-2010 at 02:50 AM.

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  2. #2
    Supporting Member Turbo Mopar Contributor Ondonti's Avatar
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    Re: Why turbos leak oil into the exhaust - With Pics!

    Ahh I guess I just missed you. Water cooled center sections really don't make much of a difference when you do a hot shutdown. The water is not able to hold much heat energy. If you imagine the density of the metal vs the water, it still cokes the oil.

    I would also think that excessively small drains on the rear bearing promote this problem. Can't really say how that center section compares to the various other center sections out there. Obviously they know about this problem when they design the turbo. Turbos originally made for a diesels may be more guilty of this.
    I also wonder about GT turbos with the ball bearing. They require very small amounts of oil so I would think that oil passages are small.

    That also shows why excessive crankcase pressure can cause the turbo to dump oil into the exhaust.
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    Hybrid booster Turbo Mopar Contributor Darkapollo's Avatar
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    Re: Why turbos leak oil into the exhaust - With Pics!

    I vote this goes in the KC.

    Great break down and explanation!

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    turbo addict BIG PSI's Avatar
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    Re: Why turbos leak oil into the exhaust - With Pics!

    Vigo,

    That was GREAT explanation and photos.

    Thank You Sir

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    Re: Why turbos leak oil into the exhaust - With Pics!

    Quote Originally Posted by Darkapollo View Post
    I vote this goes in the KC.

    Great break down and explanation!
    Ditto!!
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    Re: Why turbos leak oil into the exhaust - With Pics!

    I know i learned something.

    Great write up...i feel like i actually understand something about that damn snail in the back of my engine bay....

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    Authorized Vendor Turbo Mopar Vendor Chris W's Avatar
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    Re: Why turbos leak oil into the exhaust - With Pics!

    The photo of the split bearing housing was actually a oil cooled center section, not water cooled.

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    Re: Why turbos leak oil into the exhaust - With Pics!



    now lets see you do that with a rusty one.
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    Supporting Member Turbo Mopar Contributor omni_840's Avatar
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    Re: Why turbos leak oil into the exhaust - With Pics!

    Well done! Thanks for taking the time to take pics and explain this

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    Supporting Member Turbo Mopar Contributor
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    Re: Why turbos leak oil into the exhaust - With Pics!

    Maybe that's the reason my rebuilt engine burnt oil, I rebuilt the turbo but didn't clean it out like that.
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    Moderator Turbo Mopar Staff Vigo's Avatar
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    Re: Why turbos leak oil into the exhaust - With Pics!

    The photo of the split bearing housing was actually a oil cooled center section, not water cooled.
    When you say oil-cooled, do you mean that the way the oil drains through it was designed to do more cooling as opposed to the oil passages in our stock garretts, or just that there are no coolant passages? I am no expert on this stuff (..yet).

    Thanks for the feedback.

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    Authorized Vendor Turbo Mopar Vendor Chris W's Avatar
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    Re: Why turbos leak oil into the exhaust - With Pics!

    Quote Originally Posted by Vigo View Post
    When you say oil-cooled, do you mean that the way the oil drains through it was designed to do more cooling as opposed to the oil passages in our stock garretts, or just that there are no coolant passages? I am no expert on this stuff (..yet).

    Thanks for the feedback.
    Water cooled bearing housings are known as "Wet Bearings" and non-water cooled bearing housings are known as "Dry Bearings". Using a wet bearing housing and plugging the coolant ports is not a good idea. Oil flow/cooling is limited due to the coolant passages in the turbo. If you are only planning on running oil then use a dry bearing cartridge.

    Chris-TU

    BTW- Nice write up. It confirms many of the things we bring up in our info sheet here http://www.turbo-mopar.com/forums/sh...8&postcount=20

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    Moderator Turbo Mopar Staff Vigo's Avatar
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    Re: Why turbos leak oil into the exhaust - With Pics!

    Thanks for the info. I admit i havent seen a wide variety of turbos taken apart, and NONE of them was cut into a convenient cross-section!

    The post you linked to is good info.. have you considered submitting it to the Knowledge Center alongside your other contributions?

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    See me ride out of the sunset... Turbo Mopar Staff BadAssPerformance's Avatar
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    Re: Why turbos leak oil into the exhaust - With Pics!

    Nice work Vigo You know how to submit KC articles right?

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    Re: Why turbos leak oil into the exhaust - With Pics!

    great write up!

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    Re: Why turbos leak oil into the exhaust - With Pics!

    It's been added to the Knowledge center: http://www.turbo-mopar.com/forums/vb...&articleid=190

    Thanks Adam!
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    Moderator Turbo Mopar Staff Vigo's Avatar
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    Re: Why turbos leak oil into the exhaust - With Pics!

    Thanks Dave and everybody!

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    Re: Why turbos leak oil into the exhaust - With Pics!

    interesting, great write up, thank you

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    Re: Why turbos leak oil into the exhaust - With Pics!

    I thought you had project cars to work on Vigo? You have time for a 3 hour photo session

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    Re: Why turbos leak oil into the exhaust - With Pics!

    Excellent write up Vigo. That helps explain a lot.
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